Sequence of Palindromic Pentagonal Numbers

Sequence

The sequence of pentagonal numbers which are also palindromic begins:

$1, 5, 22, 1001, 2882, 15 \, 251, 720 \, 027, 7 \, 081 \, 807, 7 \, 451 \, 547, 26 \, 811 \, 862, \ldots$

This sequence is A002069 in the On-Line Encyclopedia of Integer Sequences (N. J. A. Sloane (Ed.), 2008).

The corresponding sequence of integers $n$ such that the $n$th pentagonal number is also palindromic begins:

$1, 2, 4, 26, 44, 101, 693, 2173, 2229, 4228, 6010, \ldots$

This sequence is A028386 in the On-Line Encyclopedia of Integer Sequences (N. J. A. Sloane (Ed.), 2008).

Sources

• 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $1001$