A002069 Palindromic pentagonal numbers.

0, 1, 5, 22, 1001, 2882, 15251, 720027, 7081807, 7451547, 26811862, 54177145, 1050660501, 1085885801, 1528888251, 2911771192, 2376574756732, 5792526252975, 5875432345785, 10810300301801, 264571020175462, 5292834004382925, 10808388588380801, 15017579397571051

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn
• base

References

• N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
• N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Links

• Bert Dobbelaere, Table of n, a(n) for n = 1..58 (terms 1..22 from N. J. A. Sloane, terms 23..30 from Robert Price)
• Patrick De Geest, More about Palindromic Pentagonals
• A. Gloden and R. A. Johnson, Problem E427, Amer. Math. Monthly, 48 (1941), 211-212.

Crossrefs

Cf. A028386, A000326.

Programs

Mathematica

Select[PolygonalNumber[5,Range[0,6*10^7]],PalindromeQ] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jan 15 2018 *)