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 A005521 #11 Jul 08 2025 00:25:51 %S A005521 1,2,4,7,12,18,26,35,46,60,75,93,113,134,157,183,212,242,275,310,346, %T A005521 385,426,470,518,568,619,672,726,782,845,910,978,1047,1121,1196,1274, %U A005521 1355,1438,1524,1613,1703,1798 %N A005521 1 + (sum of first n odd primes - n)/2. %F A005521 a(n+1) = a(n) + (prime(n+1) - 1)/2 for odd primes prime(n+1). %F A005521 a(n+2) - 2*a(n+1) + a(n) = A028334(n). - _Frank Ellermann_ %Y A005521 a(n+1) - 1 counts primorial intervals A065917. %Y A005521 Partial sums of A005521. %K A005521 nonn %O A005521 0,2 %A A005521 _N. J. A. Sloane_