a(n) is the number of subsets of {1,2,...,n} that contain exactly two odd numbers.

Terms

a(0) =0a(1) =0a(2) =2a(3) =4a(4) =12a(5) =24a(6) =48a(7) =96a(8) =160a(9) =320a(10) =480a(11) =960a(12) =1344a(13) =2688a(14) =3584a(15) =7168a(16) =9216a(17) =18432a(18) =23040a(19) =46080a(20) =56320a(21) =112640a(22) =135168a(23) =270336a(24) =319488a(25) =638976a(26) =745472a(27) =1490944a(28) =1720320a(29) =3440640