G.f. is the polynomial (Product_{k=1..19} (1 - x^(3*k)))/(1-x)^19.

Terms

a(0) =1a(1) =19a(2) =190a(3) =1329a(4) =7296a(5) =33459a(6) =133265a(7) =473366a(8) =1528436a(9) =4550899a(10) =12635095a(11) =33001366a(12) =81671804a(13) =192649265a(14) =435276035a(15) =945978271a(16) =1984585264a(17) =4031534950a(18) =7951485085a(19) =15262424710a(20) =28569031009a(21) =52246984967a(22) =93504149189