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%I #13 Jun 06 2017 14:22:36
%S 3,7,9,15,19,21,27,31,37,45,49,51,55,57,69,75,79,87,91,97,99,115,117,
%T 121,129,135,139,141,147,157,159,169,175,177,187,195,199,201,205,211,
%U 217,225,229,231,255,261,271,279,285,289,297,301,307,309,321,327,331
%N Odd numbers n such that 2n-1 is prime.
%C a(k) appears in the o.g.f. for floor(A002144(k)*n^2/4), for k >=1: x*(b(k)*(1 + x^2) + a(k)*x)/((1 - x)^3*(1 + x)), together with b(k) = (A002144(k)-1)/4 = A005098(k). - _Wolfdieter Lang_, Aug 07 2013
%F a(n) = (A002144(n) + 1)/2, n >= 1. - _Wolfdieter Lang_, Aug 07 2013
%t Select[Range[1,331,2],PrimeQ[2#-1]&] (* _Harvey P. Dale_, Feb 20 2013 *)
%o (PARI) is(n)=n%2 && isprime(2*n-1) \\ _Charles R Greathouse IV_, Jun 06 2017
%K nonn,easy
%O 1,1
%A _Roger L. Bagula_, Jun 12 2006
%E Edited by _N. J. A. Sloane_, Sep 07 2006
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