This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A059869 #12 Aug 11 2024 14:41:33
%S A059869 8,9,14,16,32
%N A059869 Numbers k such that there exist no palindromic heptagonals of length k.
%H A059869 P. De Geest, <a href="https://www.worldofnumbers.com/hepta.htm">Palindromic heptagonals</a>
%t A059869 A054910 = {0, 1, 7, 55, 616, 3553, 4774, 60606, 848848, 4615164, 5400045, 6050506, 7165445617, 62786368726, 65331413356, 73665056637, 91120102119, 345546645543, 365139931563, 947927729749, 3646334336463, 7111015101117, 717685292586717, 19480809790808491, 615857222222758516, 1465393008003935641, 8282802468642082828, 15599378333387399551, 20316023422432061302};
%t A059869 A059869[n_] := Length[Select[A054910, IntegerLength[#] == n || (n == 1 && # == 0) &]];
%t A059869 Select[Range[19], A059869[#] == 0 &] (* _Robert Price_, Apr 28 2019 *)
%Y A059869 Cf. A034822, A034307, A059868, A059870, A000566, A054971, A054910.
%K A059869 nonn,base,hard
%O A059869 1,1
%A A059869 _Patrick De Geest_, Feb 15 2000