What is New

13 November, 2012:

• The page on Unlucky 13 updated and enlarged.

• The page on Fascinating Triangular Numbers updated and enlarged.

• The page on Curious Properties of 153 updated.

• CYF NO. 40 contributions by Carlos Rivera, Maximilian Hasler, Brian Trial given.

• CYF NO. 29 Comments by - Mukesh Kr Jha given.

• CYF NO. 11 update by David Harrison given.

6 February, 2011:

• The page on Curious Properties of 153 updated.

• CYF NO. 40 contributions by B.S.Rangaswamy, Bo Gyu Jeong, Norman Luhn, Shyam Sunder Gupta given.

• CYF NO. 11 Comments by David Harrison given.

• Prime curios 19,101,449,12721,19891,12357321 and many others added.

• Integer Sequences A173542,A173543,A173544,A173545 added.

26 January, 2010:

• The page on Curious Properties of 153 updated

• Prime curios 61,67,168,173,227,349,353,378,431,434,701,729,948,1049,1471,1901,36563,60889 and many more added.

10 May, 2009:

• The page on Rare Numbers updated and enlarged. (List up to 10²⁰ )

• Prime curios 2311 and 23111...07673 (33-digits) added.

18 January, 2009:

• The page on Smith Numbers updated.

• CYF NO. 37 solutions by Luke Pebody , Jens Kruse Andersen, Donovan Johnson, Frederick Schneider given.

• CYF NO. 32 Comments by Luke Pebody given.

• Prime curios 313 and 95861...78973 (39-digits) added.

30 December, 2007:

• Integer Sequences A131306,A131316,A131535-A131552,A131604-A131606,A131609,
  A131612-A131618,A131620,A131625,A131627-A131630 added.

• CYF NO. 36 Solution by Luke Pebody, Bruno Mishutka given

14 July, 2007:

• Prime curios 4,17,1687,3283,91596...16721 (52-digits),23456...56789 (62-digits),78912...67891 (355-digits),79778...87797 (776-digits),12345...67891 (4690-digits),23456...89123 (4772-digits) added.

• CYF NO. 35 Solution by Jaroslaw Wroblewski, Frederick Schneider, Donovan Johnson given

26 January, 2007:

• The page on Cab Numbers added.

• CYF NO. 34 comments by Brian Trial, Nathan Gilbert given.

25 October, 2006:

• The page on Amicable Numbers updated.

• CYF NO. 33 solutions by Jens Kruse Andersen, Donovan Johnson, Carlos Rivera, Jacques Bernard, Nathan Gilbert, Gaurav Singh given.

• Prime curios 36,1135279341568,1311753223571113,17131175322357111317 added.

15 January, 2006:

• Prime curios 1267834459,5748693121,6913548721,12539670481,13069482857,17392546081 added.

• CYF NO. 32 Solution by Donovan Johnson given

7 November, 2005:

• The page on Amicable Numbers updated.

• CYF NO. 31 solutions by B.S.Rangaswamy, Brian Trial, Patrick De Geest given.

• Prime curios 23,41,191,1259,1291,22193,102251,3511973,4137473,5521819,5919931, 36101521,210231253,354963229,1914032047,171190210231, 19531891183017701711,18769...17689 (25-digits), 24649...25921 (25-digits) added.

1 May, 2005:

• The page on Smith Numbers updated.

• CYF NO. 30 comments by Norman Luhn given.

• Prime curios 827,6427,15131197,23252729,59575553,2527293133 and 2744337540964913 added.

11 March, 2005:

• New page on Smith Numbers added.

1 January, 2005:

• Prime curios 41,211,941,6481,235813,292319,59534743,3731292319,4916253649,576529484441,29313741434753,
  73727170696867,144121100816449,4847464544434241 and 841784729676625576529 added.

• CYF NO. 28 Solution by Jens Kruse Andersen and Donovan Johnson given.

• CYF NO. 21 Solution by Donovan Johnson

15 September, 2004:

• Prime curios 1,2,3,13,34,56,1801,5779 and many more added.

• CYF NO. 27 Solution by Carlos Rivera and Jens Kruse Andersen given.

• CYF NO. 1 Comments by Jens Kruse Andersen.

4 May, 2004:

• Prime curios 14,523,135979531,786655453628211510631 and many more added

2 March, 2004:

• CYF NO. 25 Solution by Jens Kruse Andersen (email dt 04-02-2004) and contributions by Serge Varjabedian and Patrick De Geest given.

• Prime curios 2,3,5,6,7,14,15,17,433,562,771,1049,2047,9041,65520,1235711,171311753,777...7573553 (100-digits),888...8081 (100-digits),10000...180181 (101-digits),10000...949 (101-digits),10000...2773 (101-digits),30000...3899 (101-digits),444...44969 (101-digits),777..73735353 (999-digits),8888...11101 (999-digits),10000...188001 (1000-digits),10000...18919 (1000-digits),10000...19411 (1000-digits),300..66833 (1000-digits) and many more added.

1 February, 2004:

• CYF NO. 24 Solution by Jens Kruse Andersen (email dt 02-01-2004) and Brian Trial (email dt 12-01-2004) given. Comments added.

• Prime curios 53,99999...99206 (100-digits),99999...99913 (100-digits),10000...00033 (101-digits),10000...00882 (101-digits),10000...00001 (101-digits),10000...00543 (601-digits),99999...94858 (999-digits),10000...05026 (1000-digits). added.

1 January, 2004:

• CYF NO. 23 Comments by Brian Trial (email dt 04-12-2003) added. Solution given.
• Prime curios 111,111111,2113665,11111111,111...111(12 digits),111...111(13 digits),111...111(15 digits),12345689798654321,111...111(32 digits),1000...00451(452 digits),1888...8881 (885 digits), 777..2..777(961 digits), 9888...8889(985 digits), 999..2..999 (1061 digits) added
• Page on Unlucky 13 updated.
• Page on Amicable Numbers updated.

8 November, 2003:

• Prime curios 36,227,353,626,949,13216141,509033161,10123456789,
  1023456798976543201 added

3 August, 2003:

• Prime curios 21,49,193,809,1009,2339,3793,5437,34273,101723,
  91439939,733929337,1123456987 added
• CYF NO. 20 Additional Comments by Jens Kruse Andersen (email dt 15-06-2003)

13 June, 2003:

• Page on Unlucky 13 updated.
• CYF NO. 20 Comments by Jens Kruse Andersen (email dt 24-05-2003)and Brian Trial (email dt 04-06-2003)

21 May, 2003:

• CYF NO. 19 Solved by Brian Trial (email dt 09-05-2003)
• CYF NO. 1 Comments by Phil Carmody (email dt 06-05-2003)
• CYF NO. 13 Comments by Adam Stinchcombe (email dt 05-05-2003)
• CYF NO. 17 Comments by Brian Trial (email dt 09-04-2003)

29 March, 2003:

• CYF NO. 18 Comments added. Almost solved.
• Prime curios 11,13,19,29,41,43,97,528,14269,16813...45651(507 digits),11151...11111 (666 digits), 99999...99999 (666 digits), 11111...11111 (999 digits), 99999...99999 (999 digits),11111...11111 (1000 digits),33333...33333(1000 digits) added

1 March, 2003:

• Prime curios 17,31,81,107,512,709,751,4713,5312,10000...00123 (666 digits),
  99999...98843 (666 digits), 10000... 26663 (1000 digits), 99999... 66007 (999 digits) added

1 February, 2003:

• CYF NO. 16 Solved by Jan Munch Pedersen and David Terr

1 January, 2003:

• CYF NO. 15 Solved by Brian Trial and Robin Suri

1 December, 2002:

• Page on Unlucky 13 updated.
• CYF NO. 14 Solved by Jens Kruse Andersen, Brian Trial and Robin Suri
• CYF NO. 12 Comments by Brian Trial (email dt 23-11-2002)
• CYF NO. 11 Comments by Paul Zimmermann (email dt 12-11-2002)

11 November, 2002:

• New page on My Favorite Books added.

• CYF NO. 13 Comments by Brian Trial (email dt 02-11-2002)
• CYF NO. 13 Comments by Jens Kruse Andersen (email dt 17-10-2002)

26 October, 2002:

• CYF NO. 8 Comments by Prof. François Bergeron (email dt 21-10-2002)

• A new page on Fascinating Triangular Numbers added.

5 October, 2002:

• CYF NO. 10 Solution by Brian Trial (email dt 04-10-2002)

• CYF NO.12 Results by Jens Kruse Andersen (email dt 25-09-2002)

21 September, 2002:

• CYF NO. 11 Comments by Patrick De Geest (email dt 17/18-09-2002)

• CYF NO.11 Results by Jens Kruse Andersen (email dt 18-09-2002)

6 September, 2002:

• CYF NO. 10 Comments by Brian Trial (email dt 14/25-06-2002)

• CYF NO.1 Results by Gerbicz Robert (email dt 08-07-2002)

• A new page on Smarandache Sequence of Happy Numbers added.

• Many Prime Curios added. For details see Prime Curios!

14 April, 2002:

• CYF NO. 9 Comments added . Almost Solved by Brian Trial. See Brian's Conjecture .
• Prime curios 5,19,29,207,220,567,1973,65281,112583,135799,206483,864203,975313,
  2024689,100123456789,198765432101 added

10 March, 2002:

• CYF NO. 8 Solved by Brian Trial
• CYF NO. 2 Comments added
• Prime curios 2,11,14,19,23,41,101,199,821,1297,4023,4201,6899,632148,19999999,
  191735161,1234457689,1608906624,3778888999,9876534120,10234465789,
  399899999999999,29998999999999999999999 added

17 February, 2002:

• CYF NO. 4 Solved by Carlos Rivera
• CYF NO. 7 Solved by Brian Trial
• CYF NO. 1 Comments added
• Prime curios 13,123456879,683441871,987634512,999828727,1023479856 added

10 February, 2002:

• The page on Curious Properties of 153 updated
• CYF NO. 1 & CYF NO. 2 Comments added
• Prime curios 27,140,726,3319,5879,6318,189375,211673,755968,118689518,179376463,202536181, 880346227 added

20 January, 2002:

• CYF NO. 6 Comments by Jan Munch Pedersen. He found that no solution exist for all known Amicable Numbers. (email dated 08-01-2002)
• The page on Amicable Numbers added

6 January, 2002:

• CYF NO. 5 Solved by Jan Munch Pedersen. He found that 6789783 is the smallest Odd Abundant Number not ending in 5 and also not divisible by 9. (email dated 03-01-2002)

31 December, 2001:

• The page on Curious Properties of 153 updated

25 December, 2001:

• The page on Curious Properties of 153 added

23 December, 2001:

• CYF NO. 3 Solved by Patrick De Geest. He found that n = 3088803 is the smallest multi-digit Palindromic number such that 10⁹⁹⁹ + n is prime.( email dt. 22-12-2001)

17 December, 2001:

• The page on Fascinating Squares added

9 December, 2001:

• The page on Unlucky 13 added

30 November, 2001:

• The list of all Rare Numbers up to 10^19 have been added.
• The page on Unique Numbers added