A138759 Indices for which A001203 (continued fraction for Pi) is prime.

1, 2, 9, 11, 14, 17, 18, 19, 20, 23, 27, 28, 31, 36, 37, 39, 40, 46, 48, 49, 50, 52, 59, 65, 70, 71, 72, 73, 75, 85, 86, 90, 93, 95, 97, 101, 102, 105, 106, 109, 110, 111, 118, 120, 122, 123, 124, 127, 128, 131, 132, 133, 140, 142, 145, 146, 151, 152, 153, 155, 159

Offset: 1

Author

M. F. Hasler, Mar 31 2008

Keywords

• nonn

Examples

			This sequence starts 1,2,9,11,... since the first, 2nd, 9th, 11th...
term of sequence A001203 = (3, 7, 15, 1, 292, 1, 1, 1, 2, ...) are primes.
		

Crossrefs

Cf. A001203, A005042, A107892, A138758.

Programs

Mathematica

Position[ContinuedFraction[Pi,200],?PrimeQ]//Flatten(* _Harvey P. Dale, Aug 07 2019 *)

PARI

default(realprecision,1000); t=contfrac(Pi); for( k=1,#t, isprime(t[k]) & print1(k","))

Formula

k is in A138759 <=> A001203(k) is in A000040