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

Author

J. Lowell, Aug 19 2021

Keywords

• nonn
• hard
• more

Examples

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

Links

• PrimeNet, M4703.
• Wikipedia, Lenstra elliptic-curve factorization.
• YAFU, Automated integer factorization.

Crossrefs

Cf. A049479.

Programs

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 *)