nextprime(5^n)-nextprime(2^n).

Terms

a(0) =0a(1) =4a(2) =24a(3) =116a(4) =614a(5) =3100a(6) =15562a(7) =78006a(8) =390390a(9) =1952630a(10) =9764598a(11) =48826086a(12) =244136584a(13) =1220694922a(14) =6103499226a(15) =30517545396a(16) =152587825112a(17) =762939322026