9*w(n) where : w(1)=w(2)=w(3)=1 w(n)=(w(n-1)*w(n-2)+(w(n-1)+w(n-2))/3) / w(n-3).

Terms

a(0) =9a(1) =9a(2) =9a(3) =15a(4) =23a(5) =51a(6) =93a(7) =225a(8) =429a(9) =1059a(10) =2039a(11) =5055a(12) =9753a(13) =24201a(14) =46713a(15) =115935a(16) =223799a(17) =555459a(18) =1072269a(19) =2661345a(20) =5137533a(21) =12751251a(22) =24615383a(23) =61094895a(24) =117939369a(25) =292723209a(26) =565081449a(27) =1402521135a(28) =2707467863a(29) =6719882451