cp's OEIS Frontend

A239730 Number of values of k such that 2^k - (6n+3) and (6n+3)*2^k + 1 are both prime, k < 6n+3.

%I A239730 #16 Apr 06 2014 04:21:10
%S A239730 0,0,1,3,5,3,1,3,1,5,2,1,3,2,1,1,2,5,0,3,0,1,3,2,3,2,1,5,1,1,0,0,4,1,
%T A239730 2,2,2,2,4,1,3,1,1,3,1,4,0,1,0,2,1,0,3,0,1,2,1,3,1,3,1,1,4,2,1,1,1,4,
%U A239730 2,2,4,3,1,1,3,4,6,4,1,1,1,1,1,1,0,5,0,2,2,2,1,1,2,1,1,0,1,1,0,2,1,0
%N A239730 Number of values of k such that 2^k - (6n+3) and (6n+3)*2^k + 1 are both prime, k < 6n+3.
%e A239730 a(2) = 1 because
%e A239730 1) 2^10 - (6*2+3) = 1009 and (6*2+3)*2^10 + 1 = 15361 for k = 10 < (6*2+3).
%e A239730 a(3) = 3 because
%e A239730 1) 2^5 - (6*3+3) = 11 and (6*3+3)*2^5 + 1 = 673 for k = 5 < (6*3+3);
%e A239730 2) 2^7 - (6*3+3) = 107 and (6*3+3)*2^7 + 1 = 2689 for k = 7 < (6*3+3);
%e A239730 3) 2^9 - (6*3+3) = 491 and (6*3+3)*2^9 + 1 = 10753 for k = 9 < (6*3+3).
%o A239730 (PARI) for(n=0, 120, m=0; for(k=0, 6*n+2, if(isprime(2^k-(6*n+3)) && isprime((6*n+3)*2^k+1), m++)); print1(m,", ")) \\ _Colin Barker_, Mar 26 2014
%Y A239730 Cf. A239476.
%K A239730 nonn
%O A239730 0,4
%A A239730 _Ilya Lopatin_ and _Juri-Stepan Gerasimov_, Mar 25 2014
%E A239730 a(24), a(76) and a(86) corrected by _Colin Barker_, Mar 26 2014