This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A002590 M5046 N2180 #71 Mar 15 2025 13:49:44
%S A002590 2,17,257,241,65537,61681,673,15790321,6700417,38737,4278255361,
%T A002590 2931542417,22253377,308761441,54410972897,4562284561,67280421310721,
%U A002590 2879347902817,487824887233,24517014940753,44479210368001,88959882481
%N A002590 Largest prime factor of 16^n + 1.
%D A002590 J. Brillhart et al., Factorizations of b^n +- 1. Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 2nd edition, 1985; and later supplements.
%D A002590 M. Kraitchik, Recherches sur la Théorie des Nombres. Gauthiers-Villars, Paris, Vol. 1, 1924, Vol. 2, 1929, see Vol. 2, p. 88.
%D A002590 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
%D A002590 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A002590 Max Alekseyev, <a href="/A002590/b002590.txt">Table of n, a(n) for n = 0..291</a> (terms 0..256 from Sean A. Irvine, term 277 from Tyler Busby)
%H A002590 J. Brillhart et al., <a href="http://dx.doi.org/10.1090/conm/022">Factorizations of b^n +- 1</a>, Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 3rd edition, 2002.
%H A002590 S. S. Wagstaff, Jr., <a href="http://www.cerias.purdue.edu/homes/ssw/cun/index.html">The Cunningham Project</a>
%F A002590 a(n) = A002587(4*n).
%t A002590 Join[{1},Table[FactorInteger[16^n+1][[-1,1]],{n,25}]] (* _Harvey P. Dale_, Feb 26 2012 *)
%K A002590 nonn
%O A002590 0,1
%A A002590 _N. J. A. Sloane_
%E A002590 More terms from _Don Reble_, Nov 14 2006
%E A002590 a(0) corrected by _Sean A. Irvine_, Apr 20 2014