Number of possible states when placing n tokens of 2 alternating types on 2 piles.

Terms

a(0) =1a(1) =2a(2) =4a(3) =8a(4) =15a(5) =28a(6) =52a(7) =96a(8) =177a(9) =326a(10) =600a(11) =1104a(12) =2030a(13) =3732a(14) =6858a(15) =12600a(16) =23144a(17) =42504a(18) =78048a(19) =143296a(20) =263068a(21) =482904a(22) =886392a(23) =1626912a(24) =2985943a(25) =5480012a(26) =10056946a(27) =18456056a(28) =33868851a(29) =62151788