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 A107821 #6 Apr 10 2020 06:18:49 %S A107821 1,9,2,6,5,7,4,12,11,8,10,17,3,16,14,13,15,19,18,20,21,22,24,23,27,26, %T A107821 28,25,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49, %U A107821 50,51,52,53,54,55,56,57,58,59,60,61 %N A107821 Indices of primes occurring in A107801. %H A107821 Jinyuan Wang, <a href="/A107821/b107821.txt">Table of n, a(n) for n = 1..1000</a> %F A107821 a(n) = pi(A107801(n)). %Y A107821 Cf. A107801 - A107814, A107822, A107823, A107824, A107825, A107826, A107827, A107828, A107829, A107830, A107831, A107832, A107833, A107834. %K A107821 nonn,easy %O A107821 1,2 %A A107821 _Zak Seidov_, May 24 2005