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

1,6

Links

Table of n, a(n) for n=1..105.

Formula

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

Example

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.

Mathematica

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

Prog

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

Crossrefs

Cf. A001221, A079950, A079952.

Sequence in context: A086288 A104360 A318998 * A095407 A038605 A113121

Adjacent sequences: A079948 A079949 A079950 * A079952 A079953 A079954

Keyword

nonn

Author

Reinhard Zumkeller, Jan 19 2003

Status

approved