OFFSET
1,2
PROG
(PARI) {a(n)=(matrix(n, n, r, c, if(r>=c, if(gcd(r-c+1, c)==1, 1, 0)))^-2)[n, 1]}
CROSSREFS
KEYWORD
sign
AUTHOR
Leroy Quet, Paul D. Hanna, Apr 16 2006
STATUS
approved