A394703 a(n) is the least prime factor of (3^(2^n)+1)/2.

5, 41, 17, 21523361, 926510094425921, 1716841910146256242328924544641, 257, 12289, 134382593, 59393, 790529

Offset

1,1

Comments

See A171381 for more information.

Links

Table of n, a(n) for n=1..11.

factordb.com, Status of (3^(2^12)+1)/2.

Crossrefs

Cf. A020639, A059917, A093625, A138083, A171381.

Sequence in context: A003084 A010573 A326265 * A043083 A041599 A302692

Adjacent sequences: A394700 A394701 A394702 * A394704 A394705 A394706

Keyword

nonn,hard,more

Author

Hugo Pfoertner, Mar 31 2026

Status

approved