OFFSET
1,1
COMMENTS
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
FORMULA
a(n) = (A002144(n) + 1)/2, n >= 1. - Wolfdieter Lang, Aug 07 2013
MATHEMATICA
Select[Range[1, 331, 2], PrimeQ[2#-1]&] (* Harvey P. Dale, Feb 20 2013 *)
PROG
(PARI) is(n)=n%2 && isprime(2*n-1) \\ Charles R Greathouse IV, Jun 06 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Roger L. Bagula, Jun 12 2006
EXTENSIONS
Edited by N. J. A. Sloane, Sep 07 2006
STATUS
approved