a(n) = 5^n + 5*n.

Terms

a(0) =1a(1) =10a(2) =35a(3) =140a(4) =645a(5) =3150a(6) =15655a(7) =78160a(8) =390665a(9) =1953170a(10) =9765675a(11) =48828180a(12) =244140685a(13) =1220703190a(14) =6103515695a(15) =30517578200a(16) =152587890705a(17) =762939453210