A304484 - OEIS

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

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,3

LINKS

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

MATHEMATICA

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

PROG

(Magma) A033270:=func<n|n le 1 select 0 else #PrimesUpTo(n)-1>; A:=[A033270(n):n in[1..120]]; [A[n]*A[2*n]:n in[1..#A div 2]];

(PARI) a033270(n) = max(primepi(n)-1, 0);

a(n) = a033270(n)*a033270(2*n);

CROSSREFS