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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 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.)