This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A065898 #17 Aug 10 2024 03:54:39
%S A065898 0,2,19,163,1966,26781,468178,9053660,210809338,6169323433,
%T A065898 192531847119,7161249384065,294835346718114,12720163581273289,
%U A065898 599492054060678551,31846920298131321838,1882691381652701947175,115037118886354670022443,7718754971134321663159676
%N A065898 Which composite number is the product of first n primes (the n-th primorial number)?: a(n) = k such that A002808(k) = A002110(n), or 0 if A002110(n) is not composite.
%F A065898 a(n) = A002110(n) - A000849(n) - 1. - _Amiram Eldar_, Aug 09 2024
%e A065898 a(3) = 19 because 2*3*5 = 30 = A002808(19) is the 19th composite number.
%t A065898 Table[q = Product[ Prime[i], {i, 1, n}]; q - PrimePi[q] - 1, {n, 1, 12}]
%o A065898 (PARI) a(n) = my(m = vecprod(primes(n))); m - primepi(m) - 1; \\ _Amiram Eldar_, Aug 09 2024
%Y A065898 Cf. A000720, A002808, A002110, A000849.
%K A065898 nonn
%O A065898 1,2
%A A065898 _Labos Elemer_, Nov 28 2001
%E A065898 More terms from _Robert G. Wilson v_, Nov 29 2001
%E A065898 Name clarified and a(13)-a(19) calculated from the data at A000849 and added by _Amiram Eldar_, Aug 09 2024