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Numbers k such that lambda(k) = lambda(k+2), where lambda is the Carmichael lambda function (A002322).
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%I #11 Aug 16 2024 12:20:24

%S 4,6,7,180,208,427,1183,1330,1404,1480,1584,1651,1672,2013,2695,2715,

%T 3256,3439,5250,5668,5698,5950,5955,7600,12243,13392,13715,14768,

%U 22263,22878,23347,24804,26100,30500,32940,43648,45870,46205,52548,54481,59148,59780,62719

%N Numbers k such that lambda(k) = lambda(k+2), where lambda is the Carmichael lambda function (A002322).

%H Amiram Eldar, <a href="/A333742/b333742.txt">Table of n, a(n) for n = 1..5000</a>

%e 4 is a term since lambda(4) = lambda(6) = 2.

%t Select[Range[10^4], CarmichaelLambda[#] == CarmichaelLambda[# + 2] &]

%t Position[Partition[CarmichaelLambda[Range[63000]],3,1],_?(#[[3]]==#[[1]]&),1,Heads->False]//Flatten (* _Harvey P. Dale_, Aug 16 2024 *)

%Y Cf. A001494, A002322.

%K nonn

%O 1,1

%A _Amiram Eldar_, Apr 03 2020