A002590 Largest prime factor of 16^n + 1.

2, 17, 257, 241, 65537, 61681, 673, 15790321, 6700417, 38737, 4278255361, 2931542417, 22253377, 308761441, 54410972897, 4562284561, 67280421310721, 2879347902817, 487824887233, 24517014940753, 44479210368001, 88959882481

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn

References

• J. Brillhart et al., Factorizations of b^n +- 1. Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 2nd edition, 1985; and later supplements.
• M. Kraitchik, Recherches sur la Théorie des Nombres. Gauthiers-Villars, Paris, Vol. 1, 1924, Vol. 2, 1929, see Vol. 2, p. 88.
• N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
• N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Links

• Max Alekseyev, Table of n, a(n) for n = 0..291 (terms 0..256 from Sean A. Irvine, term 277 from Tyler Busby)
• J. Brillhart et al., Factorizations of b^n +- 1, Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 3rd edition, 2002.
• S. S. Wagstaff, Jr., The Cunningham Project

Programs

Mathematica

Join[{1},Table[FactorInteger[16^n+1][[-1,1]],{n,25}]] (* Harvey P. Dale, Feb 26 2012 *)

Formula

a(n) = A002587(4*n).

Extensions

More terms from Don Reble, Nov 14 2006

a(0) corrected by Sean A. Irvine, Apr 20 2014