Expansion of Product_{1 <= i_1 <= i_2 <= i_3 <= i_4} (1 + x^(i_1*i_2*i_3*i_4)).

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =3a(5) =4a(6) =6a(7) =8a(8) =11a(9) =16a(10) =21a(11) =27a(12) =38a(13) =49a(14) =63a(15) =84a(16) =109a(17) =138a(18) =180a(19) =228a(20) =289a(21) =369a(22) =463a(23) =578a(24) =732a(25) =911a(26) =1128a(27) =1407a(28) =1741a(29) =2140