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 A256907 #19 Sep 08 2022 08:46:12 %S A256907 119,527,545,2849,3689,4487,6649,18619,26771,30377,44659,47585,50507, %T A256907 76997,83021,102167,112463,128933,138773,163877,174437,192881,193115, %U A256907 198263,217967,236441,243827,244001,254539,268067,282359,287825,298115,345059,410123,464645 %N A256907 Numbers n such that phi(n) = 3*phi(n+1). %H A256907 Mauro Fiorentini, <a href="/A256907/b256907.txt">Table of n, a(n) for n = 1..755</a> (all terms with n <= 10^9). %e A256907 phi(545) = 3*phi(546) = 432. %t A256907 Select[Range@ 1000000, EulerPhi@# == 3 EulerPhi[# + 1] &] (* _Michael De Vlieger_, Apr 12 2015 *) %o A256907 (PARI) s=[]; for(n=1, 1000000, if(eulerphi(n)==3*eulerphi(n+1), s=concat(s, n))); s \\ _Colin Barker_, Apr 12 2015 %o A256907 (Magma) [n: n in [1..2*10^6] | EulerPhi(n) eq 3*EulerPhi(n+1)]; // _Vincenzo Librandi_, Apr 13 2015 %Y A256907 Cf. A171262. %K A256907 nonn %O A256907 1,1 %A A256907 _Mauro Fiorentini_, Apr 12 2015