Number of pairs of compositions of n corresponding to a seaweed algebra of index n-3.

Terms

a(0) =6a(1) =26a(2) =80a(3) =226a(4) =600a(5) =1528a(6) =3776a(7) =9120a(8) =21632a(9) =50560a(10) =116736a(11) =266752a(12) =604160a(13) =1357824a(14) =3031040a(15) =6725632a(16) =14843904a(17) =32604160a(18) =71303168a(19) =155320320a(20) =337117184a(21) =729284608a(22) =1572864000a(23) =3382706176a(24) =7256145920a(25) =15527313408a(26) =33151778816a(27) =70632079360a(28) =150189637632a(29) =318767104000