G.f.: 9*(3x+1)/(1+2x-6x^2-27x^3).

Terms

a(0) =9a(1) =9a(2) =36a(3) =225a(4) =9a(5) =2304a(6) =1521a(7) =11025a(8) =49284a(9) =8649a(10) =576081a(11) =230400a(12) =3229209a(13) =10478169a(14) =4639716a(15) =140778225a(16) =29192409a(17) =911556864a(18) =2153052801a(19) =1951430625a(20) =33627490884a(21) =2586027609a(22) =249281516961a(23) =424895385600a(24) =715721076009