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

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.

Sequence in context: A126960 A119753 A169969 * A174350 A240476 A040140

Adjacent sequences: A291172 A291173 A291174 * A291176 A291177 A291178

Keyword

nonn

Author

Amiram Eldar, Aug 19 2017

Status

approved