A028571 Palindromes of form k*(k+9).

0, 22, 252, 2332, 20002, 26062, 29392, 63736, 68886, 2701072, 2783872, 2884882, 29122192, 253080352, 289050982, 25661316652, 237776677732, 2393677763932, 215331808133512, 218759969957812, 225588939885522, 235212787212532, 636759171957636, 682911868119286

Offset: 1

Author

Patrick De Geest

Keywords

• nonn
• base

Links

• Michael S. Branicky, Table of n, a(n) for n = 1..42
• P. De Geest, Palindromic Quasipronics of the form n(n+x)

Crossrefs

Cf. A028569, A028570.

Programs

Mathematica

Select[Table[k(k+9),{k,0,262*10^5}],PalindromeQ] (* Harvey P. Dale, Feb 13 2022 *)

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+9)):
            yield k*(k+9)
print(list(islice(agen(), 18))) # Michael S. Branicky, Jan 26 2022

Formula

a(n) = A028570(n) * (A028570(n) + 9). - Michael S. Branicky, Jan 26 2022

Extensions

a(22) and beyond from Michael S. Branicky, Jan 26 2022