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 A131807 #7 Aug 15 2023 07:45:01 %S A131807 1,2,2,3,4,4,4,5,6,7,8,8,8,9,10,11,12,12,12,13,14,15,16,16,16,16,16, %T A131807 16,16,17,18,18,18,18,18,18,18,19,20,21,22,22,22,23,24,25,26,26,26,26, %U A131807 26,26,26,27,28,29,30,31,32,32,32,33,34,35,36,37,38,38,38,38,38,39,40,40 %N A131807 Partial sums of A131377. %p A131807 P:=proc(n) local i,k,s; k:=1; s:=0; for i from 0 by 1 to n do if isprime(i) then if k=1 then k:=0; else k:=1; fi; fi; s:=s+k; print(s); od; end: P(100); %o A131807 (PARI) a(n) = sum(m=0, n, (primepi(m) % 2) == 0) \\ _Michel Marcus_, Aug 15 2023 %Y A131807 Cf. A131377. %K A131807 easy,nonn %O A131807 0,2 %A A131807 _Paolo P. Lava_ and _Giorgio Balzarotti_, Jul 18 2007