A338361 Indices of primes in A283312.

2, 4, 6, 8, 12, 15, 19, 22, 26, 32, 35, 41, 45, 48, 52, 59, 65, 68, 74, 79, 82, 88, 92, 98, 106, 111, 114, 118, 121, 126, 139, 144, 150, 153, 162, 165, 172, 178, 182, 189, 195, 198, 209, 212, 216, 219, 230, 241, 245, 248, 253, 260, 263, 274, 280, 286, 293, 296, 302, 306, 309, 320, 333

Offset: 1

Author

N. J. A. Sloane, Nov 03 2020

Keywords

• nonn

Links

• N. J. A. Sloane, Table of n, a(n) for n = 1..7099

Crossrefs

Cf. A000720, A283312.

Programs

Maple

with(NumberTheory);
A338361 := n -> ithprime(n)+n-1-pi(ithprime(n)/2);

Mathematica

A338361[n_] := Prime[n] - PrimePi[Prime[n]/2] + n - 1;
Array[A338361, 100] (* Paolo Xausa, Jan 30 2024 *)

Formula

a(n) = p(n) + n - 1 - pi(p(n)/2), where p(n) = prime(n) and pi(i) = A000720(i).