A337030 a(n) is the number of squarefree composite numbers < prime(n).

0, 0, 0, 1, 2, 2, 4, 4, 6, 7, 8, 11, 13, 14, 15, 16, 19, 19, 22, 24, 24, 27, 28, 31, 35, 35, 36, 38, 38, 40, 46, 48, 50, 51, 56, 56, 58, 61, 63, 64, 67, 67, 73, 73, 75, 75, 82, 90, 91, 91, 93, 96, 96, 99, 102, 105, 108, 108, 110, 111, 112, 117, 124, 126, 126, 127

Offset: 1

Author

Hugo Pfoertner, Aug 11 2020

Keywords

• nonn

Examples

			a(1) = a(2) = a(3) = 0 because the only composite number < 5 is the square 4.
a(4) = 1: 6 is the first squarefree composite number < prime(4) = 7.
		

Links

• Hugo Pfoertner, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A061398, A120944.

Programs

PARI

m=0;pp=0;forprime(p=2,320,forcomposite(c=pp,p,if(issquarefree(c),m++));print1(m,", ");pp=p)

Formula

a(1) = 0; a(n+1) = a(n) + A061398(n-1) for n>1.