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

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =3a(7) =4a(8) =16a(9) =20a(10) =50a(11) =60a(12) =120a(13) =140a(14) =245a(15) =280a(16) =448a(17) =504a(18) =756a(19) =840a(20) =1200a(21) =1320a(22) =1815a(23) =1980a(24) =2640a(25) =2860a(26) =3718a(27) =4004a(28) =5096a(29) =5460