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 A093948 #13 Jun 16 2025 00:49:02 %S A093948 89,8999,89999999,89999999999999999999,899999999999999999999999999999, %T A093948 89999999999999999999999999999999999999, %U A093948 8999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999 %N A093948 Primes of the form 9*10^k - 1. %C A093948 Equivalently, primes of the form 8*10^k + 9*R_k, where R_k is the repunit (A002275) of length k. %H A093948 Makoto Kamada, <a href="https://stdkmd.net/nrr/8/89999.htm#prime">Prime numbers of the form 899...999</a>. %H A093948 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>. %F A093948 a(n) = 9*10^A056725(n) - 1 = A109002(A056725(n) + 1). - _Elmo R. Oliveira_, Jun 14 2025 %Y A093948 Cf. A002275, A056725 (corresponding k). %Y A093948 Primes in A109002. %K A093948 nonn %O A093948 1,1 %A A093948 _Rick L. Shepherd_, Apr 17 2004