Number of compositions of n matching the pattern (2,1,2).

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =1a(6) =3a(7) =9a(8) =25a(9) =66a(10) =165a(11) =394a(12) =914a(13) =2068a(14) =4607a(15) =10093a(16) =21818a(17) =46592a(18) =98498a(19) =206452a(20) =429670a(21) =888818a(22) =1829005a(23) =3746802a(24) =7645511a(25) =15549306a(26) =31534322a(27) =63800562a(28) =128823111a(29) =259678348