[seqfan] Re: Definition of sigma(n) which are powers, A180162
Artur
grafix at csl.pl
Wed Aug 18 21:26:06 CEST 2010
a(11)=2752491
another 3120771,3670009,4063201
Artur
Richard Mathar pisze:
> http://oeis.org/classic/A180162 shows
> 510 = a(4) claiming it is the first N such that sigma(N)
> is a 4th power. Why isn't this 217 with sigma(217) = 256?
>
> Shouldn't the sequence start (with -1=unknown)
> 1, 2, 3, 7, 217, 21, 2667, 93, 217, 381, 651, -1, 2667, 8191, 11811, 24573
>
> Associated question: should these be merged?
>
> http://oeis.org/classic/?q=id:A180170|id:A063782
>
>
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