OFFSET
1,2
COMMENTS
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..1000 (terms 1..200 from T. D. Noe)
Florian Luca and John Ferdinands, Problem 11090: Sometimes n divides sigma_k(n), Amer. Math. Monthly 113:4 (2006), pp. 372-373.
FORMULA
Mod[ Sigma [ 4, n ], n ]=0.
EXAMPLE
n=84, Sigma[ 4,84 ] = Sum(d^4) = 53771172 = 640133*84 = 640133*n;
n=5617, Sigma[ 4,5617 ] = 995446331475844 = 5617*17722083332, a multiple of n.
MATHEMATICA
Do[If[Mod[DivisorSigma[4, n], n]==0, Print[n]], {n, 1, 2*10^6}]
Select[Range[1500000], Divisible[DivisorSigma[4, #], #]&] (* Harvey P. Dale, Jun 25 2014 *)
PROG
(PARI) is(n)=sigma(n, 4)%n==0 \\ Charles R Greathouse IV, Feb 04 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
More terms from Robert G. Wilson v, Jun 09 2000
STATUS
approved