OFFSET
1,4
PROG
(PARI) a(n)=denominator(sum(i=1, n, sum(j=1, n, sum(k=1, n, if(n-i-j-k, 0, 1)*i*j/k))))
CROSSREFS
KEYWORD
frac,nonn
AUTHOR
Benoit Cloitre, Nov 01 2002
STATUS
approved