A028558 Numbers k such that k*(k+5) is a palindrome.

0, 1, 6, 18, 24, 202, 203, 814, 2067, 2178, 2207, 20402, 25116, 64493, 82566, 207067, 2040402, 2187142, 2233097, 6887078, 79585891, 211313148, 249281986, 8161664181, 22222222222, 26331005924, 81294635989, 2008491060208, 2048192235518, 2228557243297, 2471952825156

Offset: 1

Author

Patrick De Geest

Keywords

• nonn
• base

Comments

a(34) > 10^13

Links

• Lior Manor, Table of n, a(n) for n = 1..33
• Patrick De Geest, Palindromic Quasipronics of the form n(n+x)
• Erich Friedman, What's Special About This Number? (See entries 814, 2067.)

Programs

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+5)):
            yield k
print(list(islice(agen(), 20))) # Michael S. Branicky, Jan 24 2022

Extensions

a(21)-a(27) from Michael S. Branicky, Jan 24 2022

a(28)-a(31) from Lior Manor, May 05 2024