G.f. is the polynomial (Product_{k=1..16} (1 - x^(3*k)))/(1-x)^16.

Terms

a(0) =1a(1) =16a(2) =136a(3) =815a(4) =3860a(5) =15368a(6) =53447a(7) =166652a(8) =474674a(9) =1252424a(10) =3094340a(11) =7220342a(12) =16022092a(13) =34002856a(14) =69342286a(15) =136426157a(16) =259829291a(17) =480437936a(18) =864657756a(19) =1517989041a(20) =2604677184a(21) =4375680985a(22) =7207862605a(23) =11658111130a(24) =18537088100