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 A336384 #6 Jul 31 2020 10:03:56 %S A336384 36,56,63,65,72,84,104,105,126,130,140,156,168,180,210 %N A336384 Numbers of the form k = x*y where phi(k) = 3*(phi(x) + phi(y)). %C A336384 There are 35 solutions (x, y) to phi(x*y) = 3*(phi(x) + phi(y)): (4, 14), (4, 18), (5, 13), (5, 21), (5, 26), (5, 28), (5, 36), (5, 42), (6, 6), (6, 14), (7, 9), (7, 18), (8, 13), (8, 21), (9, 7), (9, 14), (10, 13), (10, 21), (12, 13), (13, 5), (13, 8), (13, 10), (13, 12), (14, 4), (14, 6), (14, 9), (18, 4), (18, 7), (21, 5), (21, 8), (21, 10), (26, 5), (28, 5), (36, 5), (42, 5). %H A336384 GUO Rui, ZHAO Xiqing, ZHANG Lixia and XU Hongxin, <a href="http://www.cqvip.com/QK/91365X/201602/668665530.html">The positive integer solutions of euler function phi(mn) = 3^k*(phi(m) + phi(n))</a> %o A336384 (PARI) is(k) = fordiv(k, d, if(eulerphi(k) == 3*(eulerphi(d) + eulerphi(k/d)), return(1))); 0; %Y A336384 Cf. A000010, A336385. %K A336384 nonn,fini,full %O A336384 1,1 %A A336384 _Jinyuan Wang_, Jul 31 2020