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 A076820 #14 Sep 25 2018 20:50:11
%S A076820 1,1,1,1,1,2,1,1,1,2,1,2,1,2,3,1,1,2,1,2,3,2,1,2,1,2,1,2,1,3,1,1,3,2,
%T A076820 5,2,1,2,3,2,1,3,1,2,3,2,1,2,1,2,3,2,1,2,5,2,3,2,1,3,1,2,3,1,5,3,1,2,
%U A076820 3,5,1,2,1,2,3,2,7,3,1,2,1,2,1,3,5,2,3,2,1,3,7,2,3,2,5,2,1,2,3,2,1,3,1,2,5
%N A076820 Second-largest distinct prime dividing n (or 1 if n is a power of a prime).
%C A076820 The 3rd-largest is 1 except 2 at 30, 42, 60, 66, 70, ...
%H A076820 Antti Karttunen, <a href="/A076820/b076820.txt">Table of n, a(n) for n = 1..65537</a>
%F A076820 If p_1 < p_2 < ... <p_{k-1} < p_k are the distinct primes dividing n then a(n) = p_{k-1}.
%o A076820 (PARI) A076820(n) = { my(o=omega(n)); if(1>=o,1,factor(n)[o-1,1]); }; \\ _Antti Karttunen_, Sep 25 2018
%Y A076820 Cf. A006530, A119288, A292269.
%K A076820 nonn,easy,look
%O A076820 1,6
%A A076820 _R. K. Guy_, Nov 19 2002
%E A076820 More terms from _Jason Earls_ and _John W. Layman_, Nov 21 2002