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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
OFFSET
1,2
COMMENTS
Lambda(n) is the Carmichael lambda function (A002322).
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
Sequence in context: A249944 A042685 A031022 * A076646 A076617 A091791
KEYWORD
nonn
AUTHOR
Michel Lagneau, Aug 28 2011
STATUS
approved