[seqfan] Re: Definition of sigma(n) which are powers, A180162

[Andrew Weimholt]

On 8/18/10, Richard Mathar <mathar at strw.leidenuniv.nl> wrote:
>
> 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
>

Perhaps the author intends
"first N such that sigma(N) is an Nth power but not a higher power"

Andrew