A348836 a(n) is the number of primes <= prime(n)^2/2.

1, 2, 5, 9, 17, 23, 34, 41, 56, 81, 92, 124, 146, 157, 185, 222, 270, 283, 334, 368, 386, 444, 481, 548, 635, 681, 703, 753, 780, 832, 1013, 1068, 1160, 1192, 1345, 1376, 1472, 1577, 1648, 1752, 1864, 1899, 2090, 2129, 2197, 2240, 2492, 2749, 2837, 2881, 2976, 3107, 3159, 3389, 3540

Offset: 1

Author

Michel Marcus, Nov 01 2021

Keywords

• nonn

Links

• Michel Marcus, Table of n, a(n) for n = 1..2000

Crossrefs

First column of A283235.

Cf. A000040, A000720, A000879, A001248.

Programs

Mathematica

a[n_] := PrimePi[Prime[n]^2/2]; Array[a, 55] (* Amiram Eldar, Nov 01 2021 *)

PARI

a(n) = primepi(prime(n)^2/2);

Formula

a(n) = A000720(prime(n)^2/2).