Number of integer compositions of n whose first differences are not all distinct.

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =1a(5) =3a(6) =15a(7) =30a(8) =69a(9) =151a(10) =346a(11) =745a(12) =1606a(13) =3366a(14) =7035a(15) =14457a(16) =29723a(17) =60795a(18) =123545a(19) =250477a(20) =506240a(21) =1020648a(22) =2053818a(23) =4128443a(24) =8287223a(25) =16623812