a(n) = 5*3^n.

Terms

a(0) =5a(1) =15a(2) =45a(3) =135a(4) =405a(5) =1215a(6) =3645a(7) =10935a(8) =32805a(9) =98415a(10) =295245a(11) =885735a(12) =2657205a(13) =7971615a(14) =23914845a(15) =71744535a(16) =215233605a(17) =645700815a(18) =1937102445a(19) =5811307335a(20) =17433922005a(21) =52301766015a(22) =156905298045a(23) =470715894135