a(n) = 10*3^n.

Terms

a(0) =10a(1) =30a(2) =90a(3) =270a(4) =810a(5) =2430a(6) =7290a(7) =21870a(8) =65610a(9) =196830a(10) =590490a(11) =1771470a(12) =5314410a(13) =15943230a(14) =47829690a(15) =143489070a(16) =430467210a(17) =1291401630a(18) =3874204890a(19) =11622614670a(20) =34867844010a(21) =104603532030a(22) =313810596090a(23) =941431788270