OFFSET
1,2
FORMULA
{n such that n is in A100959, and 2*n + 1 is in A100959} = {n such that n is not in A001358, and 2*n + 1 is not in A001358}.
a(n) ~ n. - Charles R Greathouse IV, Jan 16 2013
EXAMPLE
a(1) = 1 because 1 is not a semiprime (the smallest semiprime is 4), and 2*1 + 1 = 3 is not a semiprime.
7 is not a semiprime, but 2*7 + 1 = 15 = 3*5 is a semiprime, so 7 is not in this sequence.
MATHEMATICA
SemiPrimeQ[n_Integer] := If[Abs[n] < 2, False, (2 == Plus @@ Transpose[FactorInteger[Abs[n]]][[2]])]; Select[Range[200], ! SemiPrimeQ[#] && ! SemiPrimeQ[2 # + 1] &] (* T. D. Noe, Jan 17 2013 *)
PROG
(PARI) is(n)=bigomega(n)!=2 && bigomega(2*n+1)!=2 \\ Charles R Greathouse IV, Jan 16 2013
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Jonathan Vos Post, Jan 16 2013
STATUS
approved