1,3

See A171381, which is the main entry for this sequence.

Table of n, a(n) for n=1..6.

(PARI) is(n)=ispseudoprime((3^(2^n)+1)/2) \\ Charles R Greathouse IV, Jun 06 2017

Cf. A093625, A171381.

Sequence in context: A327326 A170882 A116680 * A181524 A240568 A309681

Adjacent sequences: A138080 A138081 A138082 * A138084 A138085 A138086

nonn,more,hard

N. J. A. Sloane, Dec 09 2009

approved