If X_1,...,X_n is a partition of a 2n-set X into 2-blocks then a(n) is equal to the number of 4-subsets of X containing none of X_i, (i=1,...,n).

A130810

If X_1,...,X_n is a partition of a 2n-set X into 2-blocks then a(n) is equal to the number of 4-subsets of X containing none of X_i, (i=1,...,n).

Terms

    a(0) =16a(1) =80a(2) =240a(3) =560a(4) =1120a(5) =2016a(6) =3360a(7) =5280a(8) =7920a(9) =11440a(10) =16016a(11) =21840a(12) =29120a(13) =38080a(14) =48960a(15) =62016a(16) =77520a(17) =95760a(18) =117040a(19) =141680a(20) =170016a(21) =202400a(22) =239200a(23) =280800a(24) =327600a(25) =380016a(26) =438480a(27) =503440a(28) =575360a(29) =654720

External references