A113478 - OEIS

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A113478

Number of cuban primes less than 10^n.

0, 1, 4, 11, 28, 64, 173, 438, 1200, 3325, 9289, 26494, 76483, 221530, 645685, 1895983, 5593440, 16578830, 49347768, 147402214, 441641536, 1326941536, 3996900895, 12066234206, 36501753353

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OFFSET

0,3

LINKS

Table of n, a(n) for n=0..24.

Eric Weisstein's World of Mathematics, Cuban Prime

EXAMPLE

7, 19, 37, 61, 127 are the first few cuban primes, so a(1)=1 and a(2)=4.

PROG

(PARI) A113478(n)=sum(k=1, sqrt(10^n/3), isprime(3*k*(k+1)+1)) \\ M. F. Hasler, Nov 28 2007

CROSSREFS

Cf. A002407, A002504.