a(n) is the largest prime p < 2^n such that p + 2^n is also prime.

Terms

a(0) =3a(1) =5a(2) =13a(3) =29a(4) =43a(5) =113a(6) =223a(7) =509a(8) =907a(9) =2003a(10) =4051a(11) =8171a(12) =16333a(13) =32603a(14) =65437a(15) =130649a(16) =262027a(17) =524261a(18) =1048507a(19) =2097047a(20) =4194277a(21) =8388209a(22) =16776481a(23) =33554201a(24) =67108753a(25) =134217401a(26) =268435273a(27) =536869631a(28) =1073741719a(29) =2147483549