A093810 Smallest prime factor of 2^n-3.

1, 5, 13, 29, 61, 5, 11, 509, 1021, 5, 4093, 19, 16381, 5, 13, 53, 11, 5, 1048573, 773, 4194301, 5, 16777213, 479, 37, 5, 11, 536870909, 23, 5, 9241, 29, 5113, 5, 242819, 47189, 11, 5, 13, 23, 47, 5, 5927, 2087, 227, 5, 11, 19, 59, 5, 13, 2203, 36217, 5, 181

Offset: 2

Author

Yasutoshi Kohmoto, May 11 2004

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 2..626 (terms 2..200 from Vincenzo Librandi)

Crossrefs

Cf. A020639, A036563, A050414, A050415, A093817.

Programs

Mathematica

PrimeFactors[n_] := Flatten[ Table[ # [[1]], {1}] & /@ FactorInteger[n]]; Table[ PrimeFactors[2^n - 3][[1]], {n, 2, 60}] (* Robert G. Wilson v, May 24 2004 *)
FactorInteger[#][[1,1]]&/@(2^Range[2,60]-3) (* Harvey P. Dale, Aug 21 2016 *)

Formula

a(n) = A020639(A036563(n)). - Amiram Eldar, Sep 12 2022

Extensions

More terms from Robert G. Wilson v, May 24 2004