A201250 Integers k such that Sum_{i=1..k-1} (-1)^(i+1)*primepi((k-i+1)^2) = Sum_{i=1..k-1} (-1)^(i+1)*primepi((k-i)^2).

1, 3, 8, 16, 36, 38, 70, 108, 116, 148, 251, 280, 1964

Offset: 1

Author

Daniel Tisdale, Nov 28 2011

Keywords

• nonn
• more

Examples

			For k = 3,  pi(3^2)-pi(2^2) = 2 = pi(2^2)-pi(1^2), so 3 is a term.
		

Crossrefs

Cf. A000720.

Programs

PARI

isok(k) = sum(i=1, k-1, (-1)^(i+1)*primepi((k-i+1)^2)) == sum(i=1, k-1, (-1)^(i+1)*primepi((k-i)^2)); \\ Michel Marcus, Aug 16 2022

Formula

A_n = Sum_{i=1..n-1} (-1)^i * pi((n-i+1)^2);

B_n = Sum_{i=1..n-1} (-1)^i * pi((n-i)^2);

Sequence is S_n = {index(A_n - B_n) such that A_n - B_n = 0}.

Extensions

New name and a(13) from Michel Marcus, Aug 16 2022