OFFSET
1,3
COMMENTS
The reduced residue system modulo n used here is the set of numbers k from the set {0,1,...,n-1} which satisfy gcd(k,n)=1. There are phi(n) = A000010(n) such numbers k.
This is the m=4 member of a family of sequences, call them rmnS(m) (reduced mod n sum), with entries rmnS(m;n):=sum(binomial(k+m-1,m),0<=k<=n-1 with gcd(k,n)=1), m>=0, n>=1. Recall gcd(0,n)=n.
FORMULA
EXAMPLE
PROG
(PARI) a(n) = sum(k=0, n-1, if (gcd(n, k) == 1, binomial(k+3, 4))); \\ Michel Marcus, Feb 01 2016
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Wolfdieter Lang, Jun 22 2011
EXTENSIONS
More terms from Michel Marcus, Feb 01 2016
STATUS
approved