A079951 Number of primes p with prime(n) == 1 (modulo 2*p).

0, 0, 1, 1, 1, 2, 1, 1, 1, 2, 2, 2, 2, 2, 1, 2, 1, 3, 2, 2, 2, 2, 1, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 2, 2, 3, 1, 1, 2, 1, 3, 2, 2, 2, 2, 3, 2, 1, 3, 2, 2, 3, 1, 1, 1, 2, 2, 3, 3, 2, 2, 2, 2, 3, 2, 3, 3, 1, 3, 2, 1, 2, 3, 2, 1, 2, 3, 2, 3, 2, 4, 2, 2, 2, 2, 2, 3, 3, 3, 1, 1, 1, 2, 2, 1, 2, 3, 2, 3, 3, 2, 1, 2, 3

Offset: 1

Author

Reinhard Zumkeller, Jan 19 2003

Keywords

• nonn

Examples

			n=6: prime(6)=13 and 13 mod (2*2) = 1, 13 mod (2*3) = 1, 13 mod(2*5) = 3, 13 mod (2*7) = 13, therefore a(6)=2.
		

Crossrefs

Cf. A001221, A079950, A079952.

Programs

Mathematica

Table[PrimeNu[Floor[Prime[n]/2]], {n, 105}] (* Jon Maiga, Jan 06 2019 *)

PARI

a(n) = omega(prime(n)\2); \\ Michel Marcus, Jan 06 2019

Formula

a(n) = A001221(floor(A000040(n)/2)). - Jon Maiga, Jan 06 2019