OFFSET
1,2
EXAMPLE
2^4 + 2^1 + 1 = 19 is prime so a(1)=1.
2^6 + 2^2 + 1 = 67 is prime so a(2)=2.
2^8 + 2^3 + 1 = 263 is prime so a(3)=3.
MATHEMATICA
a[n_]:=2^(2*(n+1))+2^n-1; lst={}; Do[If[PrimeQ[a[n]], AppendTo[lst, n]], {n, 0, 7!}]; lst (* Vladimir Joseph Stephan Orlovsky, Jan 03 2009 *)
PROG
(PARI) is(n)=ispseudoprime(2^(2*(n+1))+2^n-1) \\ Charles R Greathouse IV, Jun 13 2017
(Magma) [k: k in [0..200] | IsPrime(2^(2*(k+1))+2^k-1)]; // Jinyuan Wang, Mar 20 2020
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Pierre CAMI, Apr 11 2005
EXTENSIONS
a(31)-a(36) from Ryan Propper, Jan 31 2008
a(37)-a(40) from Michael S. Branicky, Oct 12 2024
STATUS
approved