Expansion of Product_{i>=1, j>=1} 1 / (1 - x^(i*j*(j + 1)/2)).

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =6a(5) =9a(6) =17a(7) =23a(8) =35a(9) =54a(10) =77a(11) =108a(12) =163a(13) =221a(14) =309a(15) =436a(16) =593a(17) =800a(18) =1109a(19) =1470a(20) =1968a(21) =2642a(22) =3482a(23) =4566a(24) =6052a(25) =7848a(26) =10204a(27) =13276a(28) =17092a(29) =21924