OFFSET
1,4
FORMULA
a(3*n-1) = eulerphi(3*n)/2 - 1.
PROG
(PARI) {a(n)=local(M=matrix(n+2, n+2, r, c, if(r>=c, if(gcd(r-c+1, c)==1, 1, 0)))^2); M[n, 3]}
CROSSREFS
KEYWORD
nonn
AUTHOR
Leroy Quet, Paul D. Hanna, Apr 16 2006
STATUS
approved