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

1,2

Links

Table of n, a(n) for n=1..13.

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}.

Example

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

Prog

(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

Crossrefs

Cf. A000720.

Sequence in context: A024623 A337118 A344509 * A196373 A027291 A048952

Adjacent sequences: A201247 A201248 A201249 * A201251 A201252 A201253

Keyword

nonn,more

Author

Daniel Tisdale, Nov 28 2011

Extensions

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

Status

approved