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A291175 Numbers k such that lambda(k) = lambda(k-1) + lambda(k-2), where lambda(k) is Carmichael lambda function (A002322).

%I A291175 #24 Sep 02 2024 12:19:42
%S A291175 3,5,7,11,13,22,46,371,717,1379,1436,1437,3532,5146,12209,35652,45236,
%T A291175 58096,93932,130170,263589,327095,402056,680068,808303,814453,870689,
%U A291175 991942,1178628,1670065,1686526,2041276,2319102,2324004,3869372,4290742,4449280
%N A291175 Numbers k such that lambda(k) = lambda(k-1) + lambda(k-2), where lambda(k) is Carmichael lambda function (A002322).
%H A291175 Amiram Eldar, <a href="/A291175/b291175.txt">Table of n, a(n) for n = 1..250</a>
%e A291175 lambda(717) = 238 = 178 + 60 = lambda(716) + lambda(715), therefore 717 is in the sequence.
%t A291175 Select[Range[10^6], CarmichaelLambda[#]==CarmichaelLambda[#-1]+CarmichaelLambda[#-2]&]
%t A291175 Flatten[Position[Partition[CarmichaelLambda[Range[45*10^5]],3,1],_?(#[[1]]+#[[2]] == #[[3]]&),1,Heads->False]]+2 (* _Harvey P. Dale_, Sep 02 2024 *)
%o A291175 (Python)
%o A291175 from sympy import reduced_totient
%o A291175 A291175_list, a, b, c, n = [], 1, 1, 2, 3
%o A291175 while n < 10**6:
%o A291175     if c == a + b:
%o A291175         A291175_list.append(n)
%o A291175         print(len(A291175_list),n)
%o A291175     n += 1
%o A291175     a, b, c = b, c, reduced_totient(n) # _Chai Wah Wu_, Aug 31 2017
%Y A291175 Cf. A002322, A065557, A065900, A076136, A076251, A145469.
%K A291175 nonn
%O A291175 1,1
%A A291175 _Amiram Eldar_, Aug 19 2017