a(n) = Sum_{1 <= x_1, x_2, x_3, x_4 <= n} ( n/gcd(x_1, x_2, x_3, x_4, n) )^2.

Terms

a(0) =1a(1) =61a(2) =721a(3) =3901a(4) =15601a(5) =43981a(6) =117601a(7) =249661a(8) =525601a(9) =951661a(10) =1771441a(11) =2812621a(12) =4826641a(13) =7173661a(14) =11248321a(15) =15978301a(16) =24137281a(17) =32061661a(18) =47045521a(19) =60859501a(20) =84790321a(21) =108057901a(22) =148035361a(23) =180005581a(24) =243765601a(25) =294425101a(26) =383163121a(27) =458761501a(28) =594822481a(29) =686147581