180835

Appears in sequences

• a(n) = number of tuples (a,b,c,d) of natural numbers a,b,c,d <= n with gcd(a,b)=gcd(b,c)=gcd(c,d)=gcd(d,a)=1.at n=29A256391
• G.f.: Sum_{n>=0} (n+1)*(n+2)/2 * (x + x^n)^n.at n=69A325998