a(n) = 3*4^n + 10*2^n + 6*3^n + 5^n + 15.

Terms

a(0) =35a(1) =70a(2) =182a(3) =574a(4) =2054a(5) =7990a(6) =32942a(7) =141694a(8) =629174a(9) =2862790a(10) =13275902a(11) =62494414a(12) =297701894a(13) =1431677590a(14) =6937683662a(15) =33825224734a(16) =165731728214a(17) =815255212390