Number of 2 X 2 nonsingular 0..n matrices with rows and columns in increasing order.

Terms

a(0) =2a(1) =16a(2) =61a(3) =163a(4) =359a(5) =687a(6) =1206a(7) =1966a(8) =3040a(9) =4498a(10) =6435a(11) =8917a(12) =12077a(13) =15993a(14) =20788a(15) =26588a(16) =33542a(17) =41744a(18) =51397a(19) =62595a(20) =75543a(21) =90407a(22) =107382a(23) =126582a(24) =148292a(25) =172670a(26) =199931a(27) =230277a(28) =264005a(29) =301225