a(n) = 1*5^n + 2*4^n + 3*3^n + 4*2^n + 5*1^n.

Terms

a(0) =15a(1) =35a(2) =105a(3) =371a(4) =1449a(5) =6035a(6) =26265a(7) =117971a(8) =542409a(9) =2538515a(10) =12044025a(11) =57756371a(12) =279305769a(13) =1359736595a(14) =6654800985a(15) =32708239571a(16) =161307227529a(17) =797687136275