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 A229552 #20 Dec 09 2022 07:07:40 %S A229552 1,3,5,9,15,21,35,39,45,99,135,231,255,855,1035,1295,1539,1599,2015, %T A229552 4335,6525,9177,14399,16095,30495,55385,61131,62799,65535,72579,77615, %U A229552 110175,152649,179295,244965,299649,603459,619695,686735,1876725,2841915,3058209 %N A229552 Numbers k such that phi(k) = phi(k+2) - phi(k+1). %H A229552 Donovan Johnson and Giovanni Resta, <a href="/A229552/b229552.txt">Table of n, a(n) for n = 1..324</a> (terms < 10^13, first 100 terms from Donovan Johnson) %F A229552 a(n) = A065557(n) - 2. - _Amiram Eldar_, Dec 09 2022 %t A229552 Select[Range[10^6], EulerPhi[#] == EulerPhi[# + 2] - EulerPhi[# + 1] &] %t A229552 Position[Partition[EulerPhi[Range[31*10^5]],3,1],_?(#[[3]]-#[[2]] == #[[1]]&),1,Heads->False]//Flatten (* _Harvey P. Dale_, Nov 29 2017 *) %Y A229552 Cf. A092404, A197112, A057000, A000010, A065557. %K A229552 nonn %O A229552 1,2 %A A229552 _Vincenzo Librandi_, Sep 27 2013