a(n) = 5^n + 2.

Terms

a(0) =3a(1) =7a(2) =27a(3) =127a(4) =627a(5) =3127a(6) =15627a(7) =78127a(8) =390627a(9) =1953127a(10) =9765627a(11) =48828127a(12) =244140627a(13) =1220703127a(14) =6103515627a(15) =30517578127a(16) =152587890627a(17) =762939453127