A304483 a(n) = pi(n)*pi(2n), where pi is A000720: the prime counting function.

0, 2, 6, 8, 12, 15, 24, 24, 28, 32, 40, 45, 54, 54, 60, 66, 77, 77, 96, 96, 104, 112, 126, 135, 135, 135, 144, 144, 160, 170, 198, 198, 198, 209, 209, 220, 252, 252, 252, 264, 286, 299, 322, 322, 336, 336, 360, 360, 375, 375, 390, 405, 432, 448, 464, 464, 480, 480, 510

Offset: 1

Author

Jason Kimberley, May 13 2018

Keywords

• nonn
• easy

Links

• Jason Kimberley, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A304484(n) = A033270(n)*A033270(2n).

Cf. A291440, A291538, A291539, A291540,

Programs

Magma

A000720:=func;
A304483:=funcA000720(n)*A000720(2*n)>;
[A304483(n):n in[1..59]];

Mathematica

Array[PrimePi[#] PrimePi[2 #] &, 59] (* Michael De Vlieger, May 27 2018 *)

PARI

a(n) = primepi(n) * primepi(2*n); \\ Michel Marcus, May 27 2018