OFFSET
1,5
COMMENTS
If p is an odd prime, a(p) = p*(p^2-1)*(3*p^2-7)/480. - Robert Israel, Dec 10 2017
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..10000
John D. Baum, A Number-Theoretic Sum, Mathematics Magazine 55.2 (1982): 111-113.
MAPLE
f:= n -> add(t^4, t = select(t->igcd(t, n)=1, [$1..n/2])):
map(f, [$1..100]); # Robert Israel, Dec 10 2017
MATHEMATICA
f[n_] := Plus @@ (Select[Range[n/2], GCD[#, n] == 1 &]^4); Array[f, 41] (* Robert G. Wilson v, Dec 10 2017 *)
PROG
(PARI) a(n) = sum(j=1, n\2, (gcd(j, n)==1)*j^4); \\ Michel Marcus, Dec 10 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Dec 08 2017
STATUS
approved