Number of (1,2,3)-matching compositions of n.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =1a(7) =4a(8) =14a(9) =42a(10) =114a(11) =292a(12) =714a(13) =1686a(14) =3871a(15) =8696a(16) =19178a(17) =41667a(18) =89386a(19) =189739a(20) =399144a(21) =833290a(22) =1728374a(23) =3565148a(24) =7319212a(25) =14965880a(26) =30496302a(27) =61961380a(28) =125577752a(29) =253971555