a(n) = 15*2^n + 4^n + 5*3^n + 35.

Terms

a(0) =56a(1) =84a(2) =156a(3) =354a(4) =936a(5) =2754a(6) =8736a(7) =29274a(8) =102216a(9) =368274a(10) =1359216a(11) =5110794a(12) =19495896a(13) =75203394a(14) =292596096a(15) =1145977914a(16) =4511183976a(17) =17827536114a(18) =70660511376a(19) =280697078634