A082722 Numbers k for which there exist no palindromic 9-gonals (also known as nonagonals or enneagonals) of length k.

2, 6, 13, 14, 15, 16, 20, 25, 27, 28, 29, 30, 31, 32

Offset: 1

Author

Patrick De Geest, Apr 13 2003

Keywords

• nonn
• base
• hard

Comments

Previous name was: There exist no palindromic nonagonals (enneagonals) of length n.

Links

• P. De Geest, Palindromic nonagonals

Crossrefs

Cf. A034822, A059868, A082721, A059869, A059870, A034307.

Programs

Mathematica

A082723 = {0, 1, 9, 111, 474, 969, 6666, 18981, 67276, 4411144, 6964696, 15444451, 57966975, 448707844, 460595064, 579696975, 931929139, 994040499, 1227667221, 9698998969, 61556965516, 664248842466, 699030030996, 99451743334715499, 428987160061789824, 950178723327871059, 1757445628265447571, 4404972454542794044, 9433971680861793349, 499583536595635385994, 1637992008558002997361, 19874891310701319847891};
A082722[n_] := Length[Select[A082723, IntegerLength[#] == n || (n == 1 && # == 0) &]];
Select[Range[22], A082722[#] == 0 &] (* Robert Price, Apr 29 2019 *)

Extensions

Definition edited by Jon E. Schoenfield, Sep 15 2013