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 A291320 #23 Jul 24 2021 01:10:43
%S A291320 2,600,25584,97464,826560,1249920,50725248,1372734720,702637447680
%N A291320 Numbers k such that uphi(k) is equal to the sum of the proper unitary divisors of k.
%C A291320 Or numbers k such that usigma(k) - k = uphi(k) where usigma(k) = A034448(k) and uphi(k) = A047994(k).
%C A291320 a(10) > 10^13. - _Giovanni Resta_, May 12 2020
%e A291320 600 = 2^3*3*5^2 is a term because usigma(600) - uphi(600) = (2^3+1)*(3+1)*(5^2+1) - (2^3-1)*(3-1)*(5^2-1) = 600.
%t A291320 ok[n_] := Block[{p = Power @@@ FactorInteger[n]}, Times @@ (p + 1) == n + Times @@ (p - 1)]; Select[Range[2, 10^6], ok] (* _Giovanni Resta_, Aug 22 2017 *)
%o A291320 (PARI) usigma(n) = sumdivmult(n, d, if(gcd(d, n/d)==1, d));
%o A291320 uphi(n) = my(f=factor(n)~); prod(i=1, #f, f[1, i]^f[2, i]-1);
%o A291320 isok(n) = usigma(n)-uphi(n)==n;
%o A291320 (PARI) list(lim)=my(v=List()); forfactored(n=2,lim\1, if(sumdivmult(n, d, if(gcd(d, n[1]/d)==1, d))-prod(i=1, #n[2]~, n[2][i,1]^n[2][i,2]-1)==n[1], listput(v,n[1]))); Vec(v) \\ _Charles R Greathouse IV_, Aug 22 2017
%Y A291320 Cf. A034448, A047994, A063919.
%K A291320 nonn,more
%O A291320 1,1
%A A291320 _Altug Alkan_, Aug 22 2017
%E A291320 a(8) from _Giovanni Resta_, Aug 22 2017
%E A291320 a(9) from _Giovanni Resta_, May 12 2020