A347141 - OEIS

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

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OFFSET

1,1

LINKS

PrimeNet, M4703.

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

KEYWORD

nonn,hard,more

AUTHOR

J. Lowell, Aug 19 2021

STATUS

approved