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 A250219 #21 Dec 25 2022 20:02:46 %S A250219 -1,-1,8,0,-1,4,0,1,0,2,0,0,0,1,0,1,0,0 %N A250219 Number of times that n appears in n-th OEIS sequence (A_n), or -1 if n appears infinitely many times. %C A250219 Does a(19) equal -1? (See A000019.) %H A250219 <a href="/index/Se#selfies">Index entries for sequences whose definition involves A_n (or An)</a>. %e A250219 From _Jianing Song_, Sep 05 2018: (Start) %e A250219 a(3) = 8 since A000003(k) = 3 for k = 11, 19, 23, 27, 31, 43, 67 and 163. %e A250219 a(6) = 4 since A000006(k) = 6 for k = 12, 13, 14 and 15. %e A250219 a(10) = 2 since A000010(k) = 10 for k = 11 and 22. (End) %Y A250219 Cf. A000001, A000002, A000003, A000004, etc. %K A250219 sign,more %O A250219 1,3 %A A250219 _Eric Chen_, Dec 24 2014 %E A250219 a(3) corrected by _Jianing Song_, Sep 05 2018