G.f.: Sum_{n>=0} n! * x^(n*(n+1)/2) / Product_{k=1..n} (1 - k*x^k).

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =3a(5) =7a(6) =13a(7) =21a(8) =33a(9) =67a(10) =115a(11) =183a(12) =333a(13) =541a(14) =937a(15) =1635a(16) =2643a(17) =4327a(18) =7573a(19) =12069a(20) =20025a(21) =33427a(22) =54259a(23) =87375a(24) =144669a(25) =231541a(26) =374809a(27) =607443a(28) =970539a(29) =1545367