Perfect powers n such that (n-13)/2 is prime.

Terms

a(0) =27a(1) =1331a(2) =2187a(3) =250047a(4) =759375a(5) =2460375a(6) =12326391a(7) =13651919a(8) =20796875a(9) =33698267a(10) =51064811a(11) =52734375a(12) =63521199a(13) =80062991a(14) =86938307a(15) =139798359a(16) =156590819a(17) =170953875a(18) =190109375a(19) =219256227a(20) =377933067a(21) =502459875a(22) =625026375a(23) =642735647a(24) =679151439a(25) =707347971a(26) =756058031a(27) =985074875