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 A077099 #17 Mar 25 2020 06:52:34
%S A077099 2,2,2,1,2,2,2,1,1,2,2,8,2,6,16,1,2,3,2,2,4,2,2,4,1,6,2,4,2,16,2,1,4,
%T A077099 2,24,1,2,6,16,2,2,12,2,8,6,2,2,4,3,1,8,2,2,6,16,48,4,2,2,8,2,6,4,1,
%U A077099 12,4,2,2,4,24,2,3,2,6,4,8,12,48,2,2,1,2,2,8,4,6,16,20,2,6,8,4,4,2,48,4,2,3
%N A077099 a(n) = gcd(A051612(n), A065387(n)), where A051612(n) = sigma(n) - phi(n) and A065387(n) = sigma(n) + phi(n).
%C A077099 If a(n)=1, then n is either square or twice a square.
%H A077099 Charles R Greathouse IV, <a href="/A077099/b077099.txt">Table of n, a(n) for n = 1..10000</a>
%t A077099 sep[n_]:=Module[{s=DivisorSigma[1,n],e=EulerPhi[n]},GCD[s+e,s-e]]; Array[sep,100] (* _Harvey P. Dale_, Jun 17 2011 *)
%o A077099 (PARI) a(n)=my(f=factor(n),s=sigma(f),p=eulerphi(f)); gcd(2*p,s-p) \\ _Charles R Greathouse IV_, Jan 02 2014
%Y A077099 Cf. A000203, A000010, A051612, A065387.
%K A077099 nonn
%O A077099 1,1
%A A077099 _Labos Elemer_, Nov 06 2002
%E A077099 Edited by _Dean Hickerson_, Nov 07 2002