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 A054989 #26 Mar 07 2022 13:26:20
%S A054989 0,1,1,2,1,1,2,3,3,2,2,4,1,2,3,3,2,3,3,2,2,4,3,1,2,2,4,4,4,3,3,3,3,3,
%T A054989 3,4,4,4,5,3,5,4,5,4,4,4,4,2,3,3,2,4,3,4,2,4,4,7,4,3,3,4,4,3,3,1,3,1,
%U A054989 4,3,5,5,4,4,6,5,5,3,4,3,4,4,3,4,2,3,4
%N A054989 Number of prime divisors of -1 + (product of first n primes).
%H A054989 Amiram Eldar, <a href="/A054989/b054989.txt">Table of n, a(n) for n = 1..99</a>
%H A054989 Hisanori Mishima, <a href="http://www.asahi-net.or.jp/~KC2H-MSM/mathland/matha1/matha103.htm">Factorizations of many number sequences</a>
%H A054989 R. G. Wilson v, <a href="/A038507/a038507.txt">Explicit factorizations</a>
%e A054989 a(4)=2 because 2*3*5*7 - 1 = 209 = 11*19
%t A054989 a[q_] := Module[{x, n}, x=FactorInteger[Product[Table[Prime[i], {i, q}][[j]], {j, q}]-1]; n=Length[x]; Sum[Table[x[[i]][[2]], {i, n}][[j]], {j, n}]]
%t A054989 PrimeOmega[#] & /@ (FoldList[Times, Prime[Range[81]]] - 1) (* _Harvey P. Dale_, Mar 11 2017 *)
%Y A054989 Cf. A054988, A054990, A054991, A054992, A057588.
%K A054989 nonn,hard
%O A054989 1,4
%A A054989 Arne Ring (arne.ring(AT)epost.de), May 30 2000
%E A054989 More terms from _Robert G. Wilson v_, Mar 24 2001
%E A054989 a(42)-a(81) from _Charles R Greathouse IV_, May 07 2011
%E A054989 a(82)-a(87) from _Amiram Eldar_, Oct 03 2019