G.f.: (1+x)^2/[(1-x)^4(1-x-x^2)^3].

Terms

a(0) =1a(1) =9a(2) =46a(3) =177a(4) =571a(5) =1632a(6) =4270a(7) =10446a(8) =24244a(9) =53942a(10) =115954a(11) =242240a(12) =494087a(13) =987503a(14) =1939634a(15) =3753007a(16) =7167461a(17) =13532608a(18) =25293964a(19) =46856332a(20) =86110792a(21) =157125052a(22) =284866900a(23) =513470464a(24) =920659517a(25) =1642844485a(26) =2918680214a(27) =5164483453a(28) =9104522495a(29) =15995633440