nextprime(n) - prevprime(n).

Terms

a(0) =3a(1) =2a(2) =4a(3) =2a(4) =6a(5) =4a(6) =4a(7) =4a(8) =6a(9) =2a(10) =6a(11) =4a(12) =4a(13) =4a(14) =6a(15) =2a(16) =6a(17) =4a(18) =4a(19) =4a(20) =10a(21) =6a(22) =6a(23) =6a(24) =6a(25) =6a(26) =8a(27) =2a(28) =8a(29) =6