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A194542 Numbers n such that lambda(n) is the sum of the first k divisors of n for some k. 0
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified December 5 05:50 EST 2022. Contains 358578 sequences. (Running on oeis4.)