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
Offset: 0
Examples
7, 19, 37, 61, 127 are the first few cuban primes, so a(1)=1 and a(2)=4.
Links
- Eric Weisstein's World of Mathematics, Cuban Prime
Programs
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PARI
A113478(n)=sum(k=1,sqrt(10^n/3),isprime(3*k*(k+1)+1)) \\ M. F. Hasler, Nov 28 2007
Extensions
a(15)-a(18) from Donovan Johnson, Feb 05 2010
a(19)-a(24) from Hiroaki Yamanouchi, Oct 08 2015