a(n) = A359720(n+2,1), for n >= 0.

Terms

a(0) =2a(1) =5a(2) =21a(3) =51a(4) =170a(5) =454a(6) =1367a(7) =3776a(8) =11062a(9) =31054a(10) =89935a(11) =254654a(12) =733725a(13) =2088612a(14) =6004175a(15) =17150397a(16) =49267851a(17) =141065942a(18) =405274932a(19) =1162440833a(20) =3341173303a(21) =9596468129a(22) =27600014912a(23) =79359955225a(24) =228397685542a(25) =657335642733