A028985 Nonsquare palindromes whose sum of divisors is odd.

2, 8, 242, 20402, 24642, 2004002, 2138312, 2468642, 85099058, 200040002, 204060402, 242484242, 291080192, 20000400002, 20442824402, 24204840242, 29956665992, 88484148488, 297738837792, 2000004000002, 2004006004002, 2040608060402, 2420048400242

Offset

1,1

Comments

Palindromes of the form 2*k^2, with k a nonzero integer. - Stéphane Rézel, Jan 04 2018

Links

Stéphane Rézel, Table of n, a(n) for n = 1..68

Proof Wiki, Sigma_Function_Odd_iff_Argument_is_Square_or_Twice_Square

Mathematica

Select[Array[2 #^2 &, 10^7], PalindromeQ] (* Michael De Vlieger, Jan 10 2018 *)

Prog

(PARI) for(n=1, 10^9, my(d=digits(2*n^2)); if(d==Vecrev(d), print1(2*n^2, ", "))); \\ Joerg Arndt, Jan 10 2018

Crossrefs

Sequence in context: A009588 A338543 A125264 * A067583 A120378 A012345

Adjacent sequences: A028982 A028983 A028984 * A028986 A028987 A028988

Keyword

nonn,base

Author

Patrick De Geest

Extensions

Offset corrected and a(14)-a(21) from Donovan Johnson, Apr 25 2010

a(22)-a(23) from Donovan Johnson, Jun 16 2011

Status

approved