a(n) is the number of subsets of {1..n} that contain exactly 3 odd and 1 even numbers.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =2a(6) =3a(7) =12a(8) =16a(9) =40a(10) =50a(11) =100a(12) =120a(13) =210a(14) =245a(15) =392a(16) =448a(17) =672a(18) =756a(19) =1080a(20) =1200a(21) =1650a(22) =1815a(23) =2420a(24) =2640a(25) =3432a(26) =3718a(27) =4732a(28) =5096a(29) =6370