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

Author

Amiram Eldar, Aug 19 2017

Keywords

• nonn

Examples

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

Links

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

Crossrefs

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

Programs

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 *)

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