E.g.f.: exp( Sum_{n>=1} x^(n*(n+1)/2) / n! ).

Terms

a(0) =1a(1) =1a(2) =1a(3) =4a(4) =13a(5) =31a(6) =271a(7) =1576a(8) =6049a(9) =55693a(10) =573661a(11) =3839716a(12) =36369301a(13) =432793219a(14) =3670898323a(15) =47260464616a(16) =758854978561