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 A060668 #18 Mar 20 2025 22:31:31
%S A060668 8,20,220,272,300,368,416,456,500,656,732,848,876,1092,1160,1212,1236,
%T A060668 1328,1376,1424,1568,1624,1716,1808,2144,2244,2336,2420,2460,2480,
%U A060668 2528,2556,2768,3056,3080,3252,3320,3344,3536,3560,3612,3728,3732,3900,4016
%N A060668 Numbers k such that phi(x) = k has exactly 5 solutions.
%H A060668 Amiram Eldar, <a href="/A060668/b060668.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..1000 from T. D. Noe)
%H A060668 Max Alekseyev, <a href="https://oeis.org/wiki/User:Max_Alekseyev/gpscripts">PARI/GP Scripts for Miscellaneous Math Problems</a> (invphi.gp).
%e A060668 8 = phi(15) = phi(16) = phi(20) = phi(24) = phi(30).
%t A060668 a = Table[ 0, {5000} ]; Do[ p = EulerPhi[ n ]; If[ p < 5001, a[[ p ]]++ ], {n, 1, 15000} ]; Select[ Range[ 5000 ], a[[ # ]] == 5 & ]
%o A060668 (PARI) is(n)=sum(k=1,n,eulerphi(k)==n)==5 \\ _Charles R Greathouse IV_, Mar 03 2014
%o A060668 (PARI) is(k) = invphiNum(k) == 5 \\ _Amiram Eldar_, Nov 17 2024, using _Max Alekseyev_'s invphi.gp
%Y A060668 Cf. A000010.
%Y A060668 Number of solutions: A007617 (0), A007366 (2), A007367 (3), A060667 (4), this sequence (5), A060669 (6), A060670 (7), A060671 (8), A060672 (9), A060673 (10), A060674 (11), A060675 (12).
%K A060668 nonn
%O A060668 1,1
%A A060668 _Robert G. Wilson v_, Apr 18 2001