Number of compositions of n where the difference between largest and smallest parts equals two.

Terms

a(0) =0a(1) =0a(2) =2a(3) =3a(4) =12a(5) =20a(6) =49a(7) =95a(8) =188a(9) =366a(10) =714a(11) =1347a(12) =2565a(13) =4851a(14) =9121a(15) =17082a(16) =31960a(17) =59637a(18) =111065a(19) =206485a(20) =383411a(21) =711109a(22) =1317528a(23) =2438838a(24) =4510987a(25) =8338099a(26) =15403007a(27) =28439107a(28) =52483921a(29) =96819153