Number of compositions of n such that the cardinality of the set of parts is 2.

Terms

a(0) =0a(1) =0a(2) =2a(3) =5a(4) =14a(5) =22a(6) =44a(7) =68a(8) =107a(9) =172a(10) =261a(11) =396a(12) =606a(13) =950a(14) =1414a(15) =2238a(16) =3418a(17) =5411a(18) =8368a(19) =13297a(20) =20840a(21) =33268a(22) =52549a(23) =84120a(24) =133775a(25) =214611a(26) =343025a(27) =551064a(28) =883600a(29) =1421767