G.f.: Product_{i>=1, j>=1, k>=1, l>=1} 1/(1 - x^(i*j*k*l)).

Terms

a(0) =1a(1) =1a(2) =5a(3) =9a(4) =29a(5) =49a(6) =135a(7) =235a(8) =565a(9) =995a(10) =2177a(11) =3821a(12) =7900a(13) =13728a(14) =26974a(15) =46606a(16) =88128a(17) =150644a(18) =276283a(19) =467647a(20) =835708a(21) =1400874a(22) =2448818a(23) =4065230a(24) =6975307a(25) =11470265a(26) =19359345a(27) =31552473a(28) =52488142a(29) =84808548