a(n) = [x^n] Product_{k>=1} ((1 - x^(5*k))/(1 - x^k))^n.

Terms

a(0) =1a(1) =1a(2) =5a(3) =22a(4) =105a(5) =501a(6) =2456a(7) =12160a(8) =60801a(9) =306130a(10) =1550255a(11) =7887034a(12) =40281720a(13) =206405967a(14) =1060602800a(15) =5463059772a(16) =28199365873a(17) =145832364580a(18) =755420838614