%I #7 Aug 15 2023 07:45:01

%S 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 16,16,17,18,18,18,18,18,18,18,19,20,21,22,22,22,23,24,25,26,26,26,26,

%U 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 Partial sums of A131377.

%p 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 (PARI) a(n) = sum(m=0, n, (primepi(m) % 2) == 0) \\ _Michel Marcus_, Aug 15 2023

%Y Cf. A131377.

%K easy,nonn

%O 0,2

%A _Paolo P. Lava_ and _Giorgio Balzarotti_, Jul 18 2007