Powers of sqrt(18) rounded up.

Terms

a(0) =1a(1) =5a(2) =18a(3) =77a(4) =324a(5) =1375a(6) =5832a(7) =24744a(8) =104976a(9) =445376a(10) =1889568a(11) =8016759a(12) =34012224a(13) =144301646a(14) =612220032a(15) =2597429618a(16) =11019960576a(17) =46753733111a(18) =198359290368a(19) =841567195984