OFFSET
1,1
COMMENTS
Sequence is the intersection of the palindromic primes = A002385 = {2, 3, 5, 7, 11, 101, 131, 151, ...} and the centered 10-gonal numbers = A062786 = {1, 11, 31, 61, 101, 151, ...}. Corresponding numbers k such that 5k^2 + 5k + 1 is a term of A134462 are listed in A134463 = {1, 4, 5, 565, 475081, ...}. Note that the first 4 terms of A134463 are palindromic as well.
a(9) > 10^25. - Donovan Johnson, Feb 13 2011
a(10) > 10^39. - Patrick De Geest, May 29 2021
LINKS
Patrick De Geest, Palindromic Centered Polygonal Numbers
Eric Weisstein's World of Mathematics, Palindromic Prime
Wikipedia, Centered decagonal number.
MATHEMATICA
Do[ f=5k^2+5k+1; If[ PrimeQ[f] && FromDigits[ Reverse[ IntegerDigits[ f ] ] ] == f, Print[ f ] ], {k, 1, 500000} ]
CROSSREFS
KEYWORD
more,nonn,base
AUTHOR
Alexander Adamchuk, Oct 26 2007
EXTENSIONS
More terms from Tomas J. Bulka (tbulka(AT)rodincoil.com), Aug 30 2009
a(8) from Donovan Johnson, Feb 13 2011
a(9) from Patrick De Geest, May 29 2021
STATUS
approved