Index k of the semiprime A001358(k) = prime(n) * prime(n+1).

Terms

a(0) =2a(1) =6a(2) =13a(3) =26a(4) =48a(5) =75a(6) =103a(7) =135a(8) =199a(9) =270a(10) =338a(11) =443a(12) =508a(13) =581a(14) =706a(15) =878a(16) =1001a(17) =1124a(18) =1305a(19) =1413a(20) =1565a(21) =1764a(22) =1978a(23) =2299a(24) =2571a(25) =2724a(26) =2886a(27) =3052a(28) =3213a(29) =3710