a(n) = Sum_{k = 1..n, gcd(k,n)=1} k*(n-k).

Terms

a(0) =0a(1) =1a(2) =4a(3) =6a(4) =20a(5) =10a(6) =56a(7) =44a(8) =84a(9) =60a(10) =220a(11) =92a(12) =364a(13) =182a(14) =280a(15) =344a(16) =816a(17) =318a(18) =1140a(19) =520a(20) =840a(21) =770a(22) =2024a(23) =760a(24) =2100a(25) =1300a(26) =2196a(27) =1540a(28) =4060a(29) =1240