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 A179401 #10 Aug 19 2019 03:17:15 %S A179401 1,2,3,4,5,6,7,9,10,11,14,18,19,22,23,27,38,46,47,54,59,81,83,94,107, %T A179401 118,162,163,166,167,179,214,227,243,251,263,326,334,347,358,359,383, %U A179401 454,467,479,486,487,502,503,526,563,587,694,718,719,729,766,839,863,887,934,958 %N A179401 Numbers k such that phi(phi(k)) = lambda(lambda(k)). %H A179401 Amiram Eldar, <a href="/A179401/b179401.txt">Table of n, a(n) for n = 1..10000</a> %e A179401 1283 is in the sequence because phi(phi(1283)) = lambda(lambda(1283)) = 640. %p A179401 with(numtheory): for n from 1 to 1500 do: x:=phi(n):y:=lambda(n):if phi(x)=lambda(y) %p A179401 then printf(`%d, `,n):else fi:od: %t A179401 Select[Range[1000], EulerPhi[EulerPhi[#]] == CarmichaelLambda[CarmichaelLambda[#]] &] (* _Amiram Eldar_, Aug 19 2019 *) %Y A179401 Cf. A000010, A002322. %K A179401 nonn %O A179401 1,2 %A A179401 _Michel Lagneau_, Jan 07 2011