A304484 a(n) = A033270(n)*A033270(2n), where A033270 counts the odd primes.

0, 0, 2, 3, 6, 8, 15, 15, 18, 21, 28, 32, 40, 40, 45, 50, 60, 60, 77, 77, 84, 91, 104, 112, 112, 112, 120, 120, 135, 144, 170, 170, 170, 180, 180, 190, 220, 220, 220, 231, 252, 264, 286, 286, 299, 299, 322, 322, 336, 336, 350, 364, 390, 405, 420, 420, 435, 435, 464, 464

Offset: 1

Author

Jason Kimberley, May 15 2018

Keywords

• nonn
• easy

Links

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

Crossrefs

Cf. A304483 = A000720(n)*A000720(2n).

Programs

Magma

A033270:=func; A:=[A033270(n):n in[1..120]]; [A[n]*A[2*n]:n in[1..#A div 2]];

Mathematica

Array[(PrimePi@ # - Boole[# > 1]) (PrimePi[2 #] - Boole[2 # > 1]) &, 60] (* Michael De Vlieger, May 27 2018 *)

PARI

a033270(n) = max(primepi(n)-1, 0);
a(n) = a033270(n)*a033270(2*n);