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 A100997 #19 Jul 20 2021 12:47:30 %S A100997 2,3,4,8,21,26,35,56,61,77,200,536,695,789,904,1037,66885,70499,91835, %T A100997 100612,127239,380733,583695 %N A100997 Indices of primes in sequence defined by A(0) = 91, A(m) = 10*A(m-1) - 9 for m > 0. %C A100997 Numbers k such that 90*10^k + 1 is prime. %C A100997 Numbers k such that digit 9 followed by k >= 0 occurrences of digit 0 followed by digit 1 is prime. %C A100997 Numbers corresponding to terms <= 1037 are certified primes. %D A100997 Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467. %H A100997 Makoto Kamada, <a href="https://stdkmd.net/nrr/9/90001.htm#prime">Prime numbers of the form 900...001</a>. %H A100997 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>. %F A100997 a(n) = A056797(n) - 1. %e A100997 900001 is prime, hence 4 is a term. %o A100997 (PARI) a=91;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a-9) %o A100997 (PARI) for(n=0,1500,if(isprime(90*10^n+1),print1(n,","))) %Y A100997 Cf. A000533, A002275, A056797. %K A100997 nonn,hard,more %O A100997 1,1 %A A100997 _Klaus Brockhaus_ and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 26 2004 %E A100997 66885 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008 %E A100997 a(18)-a(21) from Kamada data by _Ray Chandler_, Apr 28 2015 %E A100997 a(22)-a(23) from Kamada data by _Mohammed Yaseen_, Jul 20 2021