Nextprime(4^n)-nextprime(2^n).

Terms

a(0) =0a(1) =2a(2) =12a(3) =56a(4) =240a(5) =994a(6) =4032a(7) =16280a(8) =65280a(9) =261626a(10) =1047552a(11) =4192266a(12) =16773160a(13) =67100670a(14) =268419048a(15) =1073709056a(16) =4294901774a(17) =17179738108a(18) =68719214620a(19) =274877382642