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 A291931 #14 Sep 07 2017 02:46:23
%S A291931 1,10,18,54,70,78,110,162,174,198,222,230,234,246,294,414,426,438,450,
%T A291931 470,486,534,594,666,702,770,846,858,882,910,1070,1158,1218,1242,1314,
%U A291931 1350,1458,1610,1722,1782,1794,1866,1914,1926,1938,1950,1998,2058,2106,2250,2442,2530,2538,2574,2590,2646,2886
%N A291931 Primitive elements of A290002.
%C A291931 Members k of A290002 such that k/2 is not in A290002.
%C A291931 Includes all members of A025192 except 2 and 6.
%H A291931 Robert Israel, <a href="/A291931/b291931.txt">Table of n, a(n) for n = 1..10000</a>
%e A291931 a(3) = 18 is in the sequence because psi(phi(18)) = phi(psi(18)) = 12 but psi(phi(9)) = 12 <> 4 = phi(psi(9)).
%p A291931 psi:= proc(n) n*mul((1+1/i[1]), i=ifactors(n)[2]) end:
%p A291931 A290002:= select(psi @ numtheory:-phi = numtheory:-phi @ psi, {$1..3000}):
%p A291931 sort(convert(A290002 minus map(`*`,A290002,2), list));
%t A291931 f[n_] := n Sum[MoebiusMu[d]^2/d, {d, Divisors@ n}]; With[{s = Select[Range[3000], f[EulerPhi@ #] == EulerPhi[f@ #] &]}, Select[s, FreeQ[s, #/2] &]] (* _Michael De Vlieger_, Sep 06 2017 *)
%Y A291931 Cf. A025192, A290002.
%K A291931 nonn
%O A291931 1,2
%A A291931 _Robert Israel_, Sep 06 2017