a(n) = Sum_{k=1..n} tau(gcd(k,n)^n), where tau(n) is the number of divisors of n.

Terms

a(0) =1a(1) =4a(2) =6a(3) =16a(4) =10a(5) =72a(6) =14a(7) =64a(8) =45a(9) =180a(10) =22a(11) =600a(12) =26a(13) =336a(14) =360a(15) =256a(16) =34a(17) =1620a(18) =38a(19) =1600a(20) =672a(21) =792a(22) =46a(23) =4752a(24) =175a(25) =1092a(26) =378a(27) =3080a(28) =58a(29) =36960