A173942 Numbers n such that sigma(lambda(n)) = lambda(sigma(n)).

1, 9, 18, 36, 63, 72, 126, 252, 504, 712, 729, 1458, 1716, 2136, 2916, 2982, 3484, 3588, 4402, 5103, 5467, 5832, 7120, 7332, 8800, 9798, 9894, 10206, 10452, 11928, 12948, 13192, 13851, 14952, 17420, 17608, 17963

Offset: 1

Author

Michel Lagneau, Nov 26 2010

Keywords

• nonn

Comments

Previous name: sigma(lambda(n)) = lambda(sigma(n)) for the sequential application of the sum of divisors of n and Carmichael lambda functions.

Numbers n such that A000203(A002322(n))=A002322(A000203(n)).

Examples

			36 is in the sequence because:
sigma(lambda(36)) = sigma(6) = 12,
lambda(sigma(36)) = lambda(91) = 12.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A123101, A002322.

Programs

Maple

with(numtheory): for n from 1 to 20000 do:if sigma(lambda(n))=lambda(sigma(n))then
  printf(`%d, `,n):else fi:od:

Mathematica

Cases[Range[20000], k_ /; DivisorSigma[1,CarmichaelLambda[k]] == CarmichaelLambda[DivisorSigma[1,k]]]

Extensions

Name edited by Michel Marcus, Mar 18 2016