A194542 Numbers n such that lambda(n) is the sum of the first k divisors of n for some k.

1, 2, 15, 18, 36, 42, 72, 78, 84, 126, 132, 140, 165, 168, 192, 200, 204, 234, 252, 260, 264, 270, 280, 288, 348, 400, 408, 440, 462, 504, 520, 546, 560, 741, 816, 825, 880, 882, 888, 912, 1040, 1044, 1248, 1464, 1470, 1632, 1638, 1692, 1710, 1749

Offset

1,2

Comments

Lambda(n) is the Carmichael lambda function (A002322).

Links

Table of n, a(n) for n=1..50.

Example

The divisors of 140 are 1, 2, 4, 5, 7, 10, 14, 20, 28, 35, 70, 140 and lambda(140) = 12 = 1 + 2 + 4 + 5; hence 140 belongs to the sequence.

Maple

with(numtheory):for n from 1 to 2500 do:x:=divisors(n):n1:=nops(x):s:=0:for k from 1 to n1 while(s<=n) do:s:=s+x[k]:if s= lambda(n) then printf(`%d, `, n):else fi:od:od:

Mathematica

Select[Range[2000], MemberQ[FoldList[Plus, 0, Divisors[#]], CarmichaelLambda[#]] &] (* T. D. Noe, Aug 29 2011 *)

Crossrefs

Cf. A002322, A072278.

Sequence in context: A249944 A042685 A031022 * A076646 A076617 A091791

Adjacent sequences: A194539 A194540 A194541 * A194543 A194544 A194545

Keyword

nonn

Author

Michel Lagneau, Aug 28 2011

Status

approved