A173600 Numbers k such that lambda(k) = tau(k).

1, 3, 10, 15, 18, 28, 63, 90, 140, 156, 234, 260, 315, 364, 408, 510, 528, 585, 672, 680, 684, 819, 880, 1120, 1248, 1920, 2080, 2912, 3420, 6120, 6528, 6660, 7140, 7920, 8400, 8568, 8892, 9324, 9840, 10710, 10880, 11088, 11424, 13260

Offset

1,2

Comments

Lambda(n) is the Carmichael lambda function (A002322). tau(n) or sigma_0(n), the number of divisors of n (A000005).

Links

Amiram Eldar, Table of n, a(n) for n = 1..1000

Example

2912 is in the sequence because lambda(2912) = tau(2912) = 24.

Maple

with(numtheory):for n from 1 to 15000 do: if lambda(n)=tau(n) then printf(`%d,
  `, n):else fi:od:

Mathematica

Select[Range[10^4], CarmichaelLambda[#] == DivisorSigma[0, #] &] (* Amiram Eldar, Jul 15 2019 *)

Prog

(PARI) isok(n) = numdiv(n) == lcm(znstar(n)[2]) \\ Miles Englezou, Feb 05 2024

Crossrefs

Cf. A000005, A002322.

Sequence in context: A226101 A141463 A134102 * A328987 A108770 A112355

Adjacent sequences: A173597 A173598 A173599 * A173601 A173602 A173603

Keyword

nonn

Author

Michel Lagneau, Nov 23 2010

Status

approved