1,1

Note that for A001333(n) to be prime, the index n must be prime or a power of 2. The indices greater than 421 yield probable primes. No others less than 80000.

Numbers n for which ((1+Sqrt[2])^n+(1-Sqrt[2])^n)/2 is prime. - Artur Jasinski (grafix(AT)csl.pl), Dec 10 2006

Eric Weisstein's World of Mathematics, Pell Number

Eric Weisstein's World of Mathematics, Integer Sequence Primes

lst={}; a=1; b=1; Do[c=a+2b; a=b; b=c; If[PrimeQ[c], AppendTo[lst, n]], {n, 2, 10000}]; lst

Do[If[PrimeQ[Expand[((1 + Sqrt[2])^n + (1 - Sqrt[2])^n)/2]], Print[n]], {n, 0, 1000}] - Artur Jasinski (grafix(AT)csl.pl), Dec 10 2006

Cf. A002203 (companion Pell numbers), A086395 (primes in A001333), A096650 (indices of prime Pell numbers).

Sequence in context: A039088 A111794 A030290 this_sequence A029447 A105362 A117331

Adjacent sequences: A099085 A099086 A099087 this_sequence A099089 A099090 A099091

hard,nonn

T. D. Noe (noe(AT)sspectra.com), Sep 24 2004

a(24) = 129127 from Eric Weisstein (eric(AT)weisstein.com), May 22, 2006

a(25) = 145969 from Eric Weisstein (eric(AT)weisstein.com), Aug 29, 2006

a(26) = 165799 from Eric Weisstein (eric(AT)weisstein.com), Nov 11, 2006

a(27) = 168677 from Eric Weisstein (eric(AT)weisstein.com), Nov 26, 2006

a(28) = 170413 from Eric Weisstein (eric(AT)weisstein.com), Dec 10, 2006

a(29) = 172243 from Eric Weisstein (eric(AT)weisstein.com), Jan 25, 2007