a(n) = 3*a(n-2) for n > 2; a(1) = 1, a(2) = 5.

Terms

a(0) =1a(1) =5a(2) =3a(3) =15a(4) =9a(5) =45a(6) =27a(7) =135a(8) =81a(9) =405a(10) =243a(11) =1215a(12) =729a(13) =3645a(14) =2187a(15) =10935a(16) =6561a(17) =32805a(18) =19683a(19) =98415a(20) =59049a(21) =295245a(22) =177147a(23) =885735a(24) =531441a(25) =2657205a(26) =1594323a(27) =7971615a(28) =4782969a(29) =23914845