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 A172104 #7 Feb 06 2019 03:48:12 %S A172104 1,2,3,3,4,5,6,6,6,7,8,9,10,10,10,11,12,13,13,13,14,14,15,15,16,17,18, %T A172104 18,18,19,19,20,21,21,22,22,23,24,24,25,25,25,25,25,26,27,28,28,28,28, %U A172104 29,30,30,30,31,32,32,33,33,33,34,35,36,36,36,37,37,38,38,39,39,40,41 %N A172104 Partial sums of A167021 where A167021(n)=1 iff 6*n+1 is prime. %C A172104 Where A167021 is the characteristic sequence: A167021(n)=1 iff 6*n+1 is prime. %o A172104 (PARI) isp(n) = isprime(6*n+1); \\ A167021 %o A172104 a(n) = sum(k=1, n, isp(k)); \\ _Michel Marcus_, Feb 06 2019 %Y A172104 Cf. A002476, A167021, A172103. %K A172104 nonn %O A172104 1,2 %A A172104 _Juri-Stepan Gerasimov_, Jan 25 2010 %E A172104 Entries checked by _R. J. Mathar_, Apr 24 2010