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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 (list; graph; refs; listen; history; text; internal format)
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.

LINKS

Table of n, a(n) for n=0..48.

T. D. Noe, Factorizations of Generalized Fermat Numbers

Eric Weisstein's World of Mathematics, Generalized Fermat Number

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

Cf. A000215, A078901.

Sequence in context: A089545 A121727 A119321 * A113482 A208853 A265889

Adjacent sequences:  A078897 A078898 A078899 * A078901 A078902 A078903

KEYWORD

easy,nonn

AUTHOR

T. D. Noe, Dec 12 2002

STATUS

approved

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Last modified August 21 06:11 EDT 2019. Contains 326162 sequences. (Running on oeis4.)