A347141 a(1) = 11; for n > 1, a(n) is the smallest prime factor of 2^a(n-1) - 1.

11, 23, 47, 2351, 4703

Offset

1,1

Links

Table of n, a(n) for n=1..5.

PrimeNet, M4703.

Wikipedia, Lenstra elliptic-curve factorization.

YAFU, Automated integer factorization.

Example

2^11 - 1 = 23*89, so the next term after 11 is 23.

Mathematica

a[1] = 11; a[n_] := a[n] = Module[{p = 3}, While[PowerMod[2, a[n - 1], p] != 1, p = NextPrime[p]]; p]; Array[a, 5] (* Amiram Eldar, Aug 19 2021 *)

Crossrefs

Cf. A049479.

Sequence in context: A096342 A066179 A217566 * A278869 A272628 A141093

Adjacent sequences: A347138 A347139 A347140 * A347142 A347143 A347144

Keyword

nonn,hard,more

Author

J. Lowell, Aug 19 2021

Status

approved