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 A076361 #32 Feb 16 2025 08:32:47
%S A076361 1,3,44,49,66,68,70,76,99,121,124,147,153,164,169,170,171,172,243,245,
%T A076361 268,275,279,361,363,387,425,475,507,529,564,603,620,644,652,724,775,
%U A076361 841,844,845,873,891,927,948,961,964,1075,1083,1132,1324,1348,1377
%N A076361 Numbers k such that d(sigma(k)) = sigma(d(k)).
%C A076361 Solutions to A076360(x) = 0.
%C A076361 Assuming Schinzel's hypothesis is true, the sequence is infinite. That conjecture implies that there are infinitely many primes p for which (p^2 + p + 1)/3 is prime. (E.g., p = 7, 13, 19, 31, 43, 73, 97, ...) For such p, we have d(sigma(p^2)) = d(p^2+p+1) = 4 and sigma(d(p^2)) = sigma(3) = 4, so p^2 is in the sequence. - _Dean Hickerson_, Jan 24 2006
%H A076361 Charles R Greathouse IV, <a href="/A076361/b076361.txt">Table of n, a(n) for n = 1..10029</a>
%H A076361 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/SchinzelsHypothesis.html">Schinzel's hypothesis</a>.
%t A076361 d0[x_] := DivisorSigma[0, x] d1[x_] := DivisorSigma[1, x] Do[s=d0[d1[n]]-d1[d0[n]]; If[s==0, Print[n]], {n, 1, 10000}]
%t A076361 Select[Range[1380],DivisorSigma[0, DivisorSigma[1, #]] == DivisorSigma[1, DivisorSigma[0, #]] &] (* _Jayanta Basu_, Mar 26 2013 *)
%o A076361 (PARI) is(n)=numdiv(sigma(n))==sigma(numdiv(n)) \\ _Charles R Greathouse IV_, Jun 25 2013
%Y A076361 Cf. A000005, A000203.
%K A076361 easy,nonn
%O A076361 1,2
%A A076361 _Labos Elemer_, Oct 08 2002