G.f.: Product_{k>=1} 1/(1-x^k)^(3*k+1).

Terms

a(0) =1a(1) =4a(2) =17a(3) =58a(4) =186a(5) =546a(6) =1532a(7) =4082a(8) =10502a(9) =26096a(10) =63075a(11) =148536a(12) =342096a(13) =771744a(14) =1709299a(15) =3721792a(16) =7978972a(17) =16860328a(18) =35155475a(19) =72393580a(20) =147351112a(21) =296657196a(22) =591141762a(23) =1166570452a(24) =2281101159a(25) =4421781894a(26) =8500806341a(27) =16214549920a(28) =30696683828