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A028985 Nonsquare palindromes whose sum of divisors is odd. 1
2, 8, 242, 20402, 24642, 2004002, 2138312, 2468642, 85099058, 200040002, 204060402, 242484242, 291080192, 20000400002, 20442824402, 24204840242, 29956665992, 88484148488, 297738837792, 2000004000002, 2004006004002, 2040608060402, 2420048400242 (list; graph; refs; listen; history; text; internal format)
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: A091503 A009588 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

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Last modified February 20 21:43 EST 2019. Contains 320355 sequences. (Running on oeis4.)