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 A248795 #36 Jul 28 2025 08:57:25
%S A248795 1,3,5,15,255,65535,2200694,2619705,6372794,40588485,76466985,
%T A248795 81591194,118018094,206569605,470542485,525644385,726638834,791937614,
%U A248795 971122514,991172805,1268457014,1384822005,1613055045,1709460753,1861556654,1872619665,2507927414,2659263945
%N A248795 Numbers k such that Product_{d|k} phi(d) = Product_{d|(k+1)} phi(d) where phi(x) = Euler totient function (A000010).
%C A248795 Numbers k such that A029940(k) = A029940(k+1).
%C A248795 4294967295 is in this sequence.
%F A248795 a(n) = A248796(n) - 2.
%e A248795 15 is in the sequence because A029940(15) = A029940(16) = 64.
%t A248795 a248795[n_Integer] := Select[Range[n],
%t A248795 Product[EulerPhi[i], {i, Divisors[#]}] ==
%t A248795 Product[EulerPhi[j], {j, Divisors[# + 1]}] &]; a248795[10^5] (* _Michael De Vlieger_, Nov 30 2014 *)
%o A248795 (Magma) [n: n in [1..100000] | (&*[EulerPhi(d): d in Divisors(n)]) eq (&*[EulerPhi(d): d in Divisors(n+1)])];
%o A248795 (PARI) lista(nn) = {d = divisors(1); vcur = prod(k=1, #d, eulerphi(d[k])); for (n=2, nn, d = divisors(n); vnext = prod(k=1, #d, eulerphi(d[k])); if (vnext == vcur, print1(n-1, ", ")); vcur = vnext;);} \\ _Michel Marcus_, Nov 23 2014
%Y A248795 Cf. A000010, A019434, A029940, A248796.
%K A248795 nonn
%O A248795 1,2
%A A248795 _Jaroslav Krizek_, Nov 19 2014
%E A248795 a(7)-a(9) from _Michel Marcus_, Nov 21 2014
%E A248795 a(10)-a(20) from _Michel Marcus_, Nov 23 2014
%E A248795 More terms from _Jinyuan Wang_, Jul 27 2025