A028561 Numbers k such that k*(k+6) is a palindrome.

0, 1, 5, 22, 137, 273, 715, 863, 2731, 8541, 486618, 877173, 1378507, 1731746, 2273915, 2436099, 5401396, 7153679, 7560069, 14529486, 23887419, 23975475, 73114035, 84890503, 88837611, 235680755, 235769755, 272515513, 440021417, 782357262, 1414071397, 2352019439

Offset: 1

Author

Patrick De Geest

Keywords

• nonn
• base

Links

• Michael S. Branicky, Table of n, a(n) for n = 1..35
• Patrick De Geest, Palindromic Quasipronics of the form n(n+x)
• Erich Friedman, What's Special About This Number? (See entries 863, 8541.)

Crossrefs

Cf. A002113, A028560, A028562.

Programs

Mathematica

Select[Range[0,24*10^6],PalindromeQ[#(#+6)]&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Sep 04 2017 *)

Python

from itertools import count, islice
def ispal(n): s = str(n); return s == s[::-1]
def agen():
    for k in count(0):
        if ispal(k*(k+6)):
            yield k
print(list(islice(agen(), 22))) # Michael S. Branicky, Jan 25 2022

Extensions

a(23) and beyond from Michael S. Branicky, Jan 25 2022