A113478 - OEIS

%I #13 Oct 09 2015 04:57:43

%S 0,1,4,11,28,64,173,438,1200,3325,9289,26494,76483,221530,645685,

%T 1895983,5593440,16578830,49347768,147402214,441641536,1326941536,

%U 3996900895,12066234206,36501753353

%N Number of cuban primes less than 10^n.

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/CubanPrime.html">Cuban Prime</a>

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

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

%Y Cf. A002407, A002504.

%K nonn,more

%O 0,3

%A _Eric W. Weisstein_, Jan 10 2006

%E a(15)-a(18) from _Donovan Johnson_, Feb 05 2010

%E a(19)-a(24) from _Hiroaki Yamanouchi_, Oct 08 2015