Function: sigma
Section: number_theoretical
C-Name: gsumdivk
Prototype: GD1,L,
Help: sigma(x,{k=1}): sum of the k-th powers of the divisors of x. k is
 optional and if omitted is assumed to be equal to 1.
Description:
 (int, ?1):int           sumdiv($1)
 (int, 0):int            numbdiv($1)
 (gen, ?1):gen           gsumdiv($1)
 (gen, 0):gen            gnumbdiv($1)
 (int, small):int        sumdivk($1, $2)
 (gen, small):gen        gsumdivk($1, $2)
Doc: sum of the $k^{\text{th}}$ powers of the positive divisors of $|x|$. $x$
 and $k$ must be of type integer.
 The function accepts vector/matrices arguments for $x$, and is then applied
 componentwise.
Variant: Also available are
 \fun{GEN}{gsumdiv}{GEN n} ($k = 1$), \fun{GEN}{sumdivk}{GEN n,long k}
 ($n$ a \typ{INT}) and \fun{GEN}{sumdiv}{GEN n} ($k = 1$, $n$ a \typ{INT})
