A028503 Numbers k such that k*(k+2) is a palindrome.

0, 1, 2, 9, 17, 23, 64, 75, 99, 191, 204, 999, 1747, 1907, 2365, 2966, 5731, 9999, 18991, 20564, 99999, 174601, 174747, 179317, 243063, 293786, 552101, 999999, 1868287, 2967032, 9200156, 9999999, 22765895, 31552659, 93809716, 99999999, 185812387, 999999999

Offset: 1

Author

Patrick De Geest

Keywords

• nonn
• base

Links

• Giovanni Resta, Table of n, a(n) for n = 1..53
• P. De Geest, Palindromic quasipronic numbers of the form n(n+2)

Crossrefs

Cf. A005563, A028504, A070253.

Programs

Mathematica

palQ[n_] := Block[{d = IntegerDigits[n]}, d == Reverse[d]]; Select[Range[0, 10^5], palQ[# (# + 2)] &] (* Giovanni Resta, Aug 29 2018 *)

Formula

a(n) = A070253(n) - 1. a(n) * (a(n) + 2) = A028504(n). - Giovanni Resta, Aug 29 2018

Extensions

More terms from Giovanni Resta, Aug 28 2018