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A304484
a(n) = A033270(n)*A033270(2n), where A033270 counts the odd primes.
3
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
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
KEYWORD
nonn,easy
AUTHOR
Jason Kimberley, May 15 2018
STATUS
approved