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 A305398 #7 Jun 02 2018 21:29:29
%S A305398 1,2,3,4,5,6,6,7,7,9,10,12,11,12,13,15,16,15,16,18,19,20,21,22,22,23,
%T A305398 25,27,26,29,29,27,31,33,32,34,36,36,38,39,35,38,40,43,38,44,46,46,45,
%U A305398 48,50,49,49,51,50,54,54,57,58,56,57,58,58,63,62,64,63,67,64,68,69,69,70,69,74,76,71,73,76,78,80,79,80,81,84,84,83,87,88,86,88
%N A305398 Index of the least prime not dividing p-1, where p = A073918(n) is the smallest prime such that p-1 has n distinct prime factors.
%C A305398 For 0 <= n <= 5, A073918(n) = A002110(n) + 1 = prime(n)# + 1, therefore a(n) = n + 1. From n >= 6 on, some smaller primes are missing in the factorization of A073918(n) - 1, whence a(n) <= n.
%C A305398 This is related to the conjecture formulated in A073918, that for any m there is K(m) such that prime(m)# | A073918(k)-1 for all k >= K(m): This conjecture is equivalent to lim inf a(n) = oo.
%e A305398 For 0 <= n <= 5, the smallest prime p = A073918(n) such that p-1 has n distinct prime factors is p = prime(n)# + 1, therefore a(n) = n + 1 is the index of the smallest prime not dividing p - 1.
%e A305398 For n = 6, the smallest prime p such that p - 1 has 6 distinct prime factors is prime(5)#*prime(8) + 1, therefore a(n) = 6.
%o A305398 (PARI) a(n)={(n=factor(A073918(n)-1)[,1])&& for(i=2,#n,n[i]>prime(i)&&return(i)); #n+1} \\ For illustration; it is more efficient to adapt code from A073918 to compute the sequence.
%Y A305398 Cf. A073918, A002110.
%K A305398 nonn
%O A305398 0,2
%A A305398 _M. F. Hasler_, May 31 2018