A291175 - OEIS

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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).

3, 5, 7, 11, 13, 22, 46, 371, 717, 1379, 1436, 1437, 3532, 5146, 12209, 35652, 45236, 58096, 93932, 130170, 263589, 327095, 402056, 680068, 808303, 814453, 870689, 991942, 1178628, 1670065, 1686526, 2041276, 2319102, 2324004, 3869372, 4290742, 4449280

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OFFSET

1,1

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..250

EXAMPLE

lambda(717) = 238 = 178 + 60 = lambda(716) + lambda(715), therefore 717 is in the sequence.

MATHEMATICA

Select[Range[10^6], CarmichaelLambda[#]==CarmichaelLambda[#-1]+CarmichaelLambda[#-2]&]

Flatten[Position[Partition[CarmichaelLambda[Range[45*10^5]], 3, 1], _?(#[[1]]+#[[2]] == #[[3]]&), 1, Heads->False]]+2 (* Harvey P. Dale, Sep 02 2024 *)

PROG

(Python)

from sympy import reduced_totient

A291175_list, a, b, c, n = [], 1, 1, 2, 3

while n < 10**6:

if c == a + b:

A291175_list.append(n)

print(len(A291175_list), n)

n += 1

a, b, c = b, c, reduced_totient(n) # Chai Wah Wu, Aug 31 2017

CROSSREFS

Cf. A002322, A065557, A065900, A076136, A076251, A145469.