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 A078150 #13 Jun 19 2025 10:43:23
%S A078150 3,5,7,17,13,35,31,37,113,77,61,221,185,143,211,209,181,287,241,577,
%T A078150 1729,403,421,1297,1057,1001,2113,779,1009,899,1321,1917,5629,1333,
%U A078150 1801,2233,7125,1763,2161,2993,4433,4851,3737,3311,51319,2623,2521
%N A078150 Smallest k such that d(phi(k)) - phi(d(k)) = n, where d(k) = A000005(k) and phi(k) = A000010(k).
%t A078150 f[x_] := DivisorSigma[0, EulerPhi[x]]-EulerPhi[DivisorSigma[0, x]] t=Table[0, {100}]; Do[s=f[n]; If[s<101&&t[[s]]==0, t[[s]]=n], {n, 1, 100000}]; t
%o A078150 (PARI) a(n) = my(k=1); while (numdiv(eulerphi(k)) - eulerphi(numdiv(k)) != n, k++); k; \\ _Michel Marcus_, Jun 19 2025
%Y A078150 Cf. A000005, A000010.
%Y A078150 Least inverse of A385122.
%K A078150 easy,nonn
%O A078150 1,1
%A A078150 _Labos Elemer_, Nov 26 2002