Primes p with p-1, p+1, prime(p)-1 and prime(p)+1 all practical.

Terms

a(0) =3a(1) =7a(2) =31a(3) =89a(4) =199a(5) =8009a(6) =11551a(7) =20129a(8) =23549a(9) =38609a(10) =47501a(11) =67231a(12) =96221a(13) =97001a(14) =103409a(15) =111871a(16) =120473a(17) =131071a(18) =143261a(19) =146681a(20) =168869a(21) =174761a(22) =183091a(23) =193951a(24) =196181a(25) =208279a(26) =208961a(27) =219727a(28) =229769a(29) =237691