a(n) = prime(prime(prime(n) - 1) - 1) - 1, where prime(n) = n-th prime.

Terms

a(0) =1a(1) =2a(2) =12a(3) =36a(4) =106a(5) =150a(6) =238a(7) =280a(8) =396a(9) =576a(10) =612a(11) =862a(12) =1020a(13) =1068a(14) =1212a(15) =1492a(16) =1732a(17) =1810a(18) =2088a(19) =2346a(20) =2410a(21) =2712a(22) =2902a(23) =3220a(24) =3582a(25) =3906a(26) =4020a(27) =4210a(28) =4336a(29) =4512