A131808 Partial sums of A131378.

0, 0, 1, 1, 1, 2, 3, 3, 3, 3, 3, 4, 5, 5, 5, 5, 5, 6, 7, 7, 7, 7, 7, 8, 9, 10, 11, 12, 13, 13, 13, 14, 15, 16, 17, 18, 19, 19, 19, 19, 19, 20, 21, 21, 21, 21, 21, 22, 23, 24, 25, 26, 27, 27, 27, 27, 27, 27, 27, 28, 29, 29, 29, 29, 29, 29, 29, 30, 31, 32, 33, 33, 33, 34, 35, 36, 37, 38

Offset

0,6

Links

Table of n, a(n) for n=0..77.

Maple

P:=proc(n) local i, k, s; k:=0; 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);

Mathematica

nxt[{n_, a_}]:={n+1, Which[a==0&&PrimeQ[n+1], 1, a==1&&PrimeQ[n+1], 0, True, a]}; Accumulate[NestList[nxt, {0, 0}, 100][[All, 2]]] (* Harvey P. Dale, Jul 19 2019 *)

Prog

(PARI) a(n) = sum(m=0, n, (primepi(m) % 2) == 1); \\ Michel Marcus, Aug 15 2023

Crossrefs

Cf. A131378.

Sequence in context: A189635 A109785 A058224 * A196183 A200264 A104406

Adjacent sequences: A131805 A131806 A131807 * A131809 A131810 A131811

Keyword

easy,nonn

Author

Paolo P. Lava and Giorgio Balzarotti, Jul 18 2007

Status

approved