A179401 - OEIS

%I #10 Aug 19 2019 03:17:15

%S 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 118,162,163,166,167,179,214,227,243,251,263,326,334,347,358,359,383,

%U 454,467,479,486,487,502,503,526,563,587,694,718,719,729,766,839,863,887,934,958

%N Numbers k such that phi(phi(k)) = lambda(lambda(k)).

%H Amiram Eldar, <a href="/A179401/b179401.txt">Table of n, a(n) for n = 1..10000</a>

%e 1283 is in the sequence because phi(phi(1283)) = lambda(lambda(1283)) = 640.

%p with(numtheory): for n from 1 to 1500 do: x:=phi(n):y:=lambda(n):if phi(x)=lambda(y)

%p   then printf(`%d, `,n):else fi:od:

%t Select[Range[1000], EulerPhi[EulerPhi[#]] == CarmichaelLambda[CarmichaelLambda[#]] &] (* _Amiram Eldar_, Aug 19 2019 *)

%Y Cf. A000010, A002322.

%K nonn

%O 1,2

%A _Michel Lagneau_, Jan 07 2011