a(n) = 5^n + 2^n - 1^n.

Terms

a(0) =1a(1) =6a(2) =28a(3) =132a(4) =640a(5) =3156a(6) =15688a(7) =78252a(8) =390880a(9) =1953636a(10) =9766648a(11) =48830172a(12) =244144720a(13) =1220711316a(14) =6103532008a(15) =30517610892a(16) =152587956160a(17) =762939584196