1,1

a(n) is an intersection of the Palindromic primes = A002385(n) = {2, 3, 5, 7, 11, 101, 131, 151, ...} and the Centered 10-gonal numbers = A062786(n) = {1, 11, 31, 61, 101, 151, ...}. Corresponding numbers n such that 5n^2 + 5n + 1 is a term of A134462 are listed in A134463 = {1, 4, 5, 565, 475081, ...}. Note that the first 4 terms of A134463 are the palindromes.

Eric Weisstein, Link to a section of The World of Mathematics. Palindromic Prime.

Wikipedia: Centered decagonal number.

Do[ f=5k^2+5k+1; If[ PrimeQ[f] && FromDigits[ Reverse[ IntegerDigits[ f ] ] ] == f, Print[ f ] ], {k, 1, 500000} ]

Cf. A002385 = Palindromic primes. Cf. A062786 = Centered 10-gonal numbers. Cf. A090562 = Primes of the form 5k^2 + 5k + 1. Cf. A090563 = Values of n such that 5n^2 + 5n + 1 is a prime. Cf. A134463 = Values of n such that 5n^2 + 5n + 1 is a palindromic prime.

Sequence in context: A052035 A083144 A058411 this_sequence A118592 A089716 A084987

Adjacent sequences: A134459 A134460 A134461 this_sequence A134463 A134464 A134465

more,nonn,base

Alexander Adamchuk (alex(AT)kolmogorov.com), Oct 26 2007