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A078900
Generalized Fermat numbers of the form (k+1)^2^m + k^2^m, with m>0.
3
5, 13, 17, 25, 41, 61, 85, 97, 113, 145, 181, 221, 257, 265, 313, 337, 365, 421, 481, 545, 613, 685, 761, 841, 881, 925, 1013, 1105, 1201, 1301, 1405, 1513, 1625, 1741, 1861, 1921, 1985, 2113, 2245, 2381, 2521, 2665, 2813, 2965, 3121, 3281, 3445, 3613, 3697
OFFSET
0,1
COMMENTS
It can be shown that, like the Fermat numbers, two of these generalized Fermat numbers are coprime if they have the same base k. However, unlike the Fermat numbers (which are conjectured to be squarefree), these generalized Fermat numbers are not necessarily squarefree for k > 1. Riesel tabulates some prime factors of generalized Fermat numbers for k <= 5.
For k=1, these are the Fermat numbers A000215. See A078901 for the case m>1, which excludes the sum of consecutive squares. By Legendre's theorem (Riesel, p. 165), the prime factors of a generalized Fermat number are of the form 1 + f 2^(m+1) for some integer f.
REFERENCES
H. Riesel, "Prime numbers and computer methods for factorization," Second Edition, Progress in Mathematics, Vol. 126, Birkhauser, Boston, 1994, pp. 417-425.
MATHEMATICA
mx=5000; maxK=Ceiling[Sqrt[mx/2]]; maxM=Ceiling[Log[2, Log[2, mx]]]; lst={}; Do[gf=(k+1)^2^m+k^2^m; If[gf<mx, AppendTo[lst, gf]], {k, maxK}, {m, 1, maxM}]; lst1=Union[lst]
CROSSREFS
Sequence in context: A089545 A121727 A119321 * A113482 A208853 A265889
KEYWORD
easy,nonn
AUTHOR
T. D. Noe, Dec 12 2002
STATUS
approved