Number of distinct products i*j*k*l for 1 <= i <= j <= k <= l <= n.

Terms

a(0) =1a(1) =5a(2) =15a(3) =25a(4) =55a(5) =75a(6) =140a(7) =175a(8) =225a(9) =275a(10) =448a(11) =504a(12) =770a(13) =882a(14) =1022a(15) =1134a(16) =1626a(17) =1782a(18) =2460a(19) =2670a(20) =2970a(21) =3270a(22) =4345a(23) =4565a(24) =5135a(25) =5585a(26) =6100a(27) =6505a(28) =8338a(29) =8679