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

1,3

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

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

Sequence in context: A283474 A206370 A297416 * A095162 A075723 A294496

Adjacent sequences: A304481 A304482 A304483 * A304485 A304486 A304487

Keyword

nonn,easy

Author

Jason Kimberley, May 15 2018

Status

approved