a(n) = A000081(n+1) - 2*A000081(n).

Terms

a(0) =1a(1) =2a(2) =8a(3) =19a(4) =56a(5) =147a(6) =404a(7) =1082a(8) =2954a(9) =8001a(10) =21865a(11) =59759a(12) =164085a(13) =451465a(14) =1246358a(15) =3448876a(16) =9569376a(17) =26611517a(18) =74172493a(19) =207159274a(20) =579724677a(21) =1625287220a(22) =4564461309a(23) =12839597611a(24) =36172421770a(25) =102053738981a(26) =288317817804a(27) =815591326704