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 A268177 Numbers m such that Sum_{i=1..q} 1/lambda(d(i)) is an integer, where d(i) are the q divisors of m and lambda is the Carmichael lambda function (A002322). 2
 1, 2, 6, 8, 12, 15, 24, 28, 30, 40, 70, 84, 112, 120, 140, 210, 240, 252, 280, 315, 336, 351, 357, 360, 420, 550, 630, 684, 702, 714, 836, 840, 884, 912, 952, 988, 1092, 1100, 1120, 1140, 1364, 1386, 1650, 1710, 1820, 2002, 2040, 2088, 2090, 2200, 2394, 2484 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS The corresponding integers are 1, 2, 3, 3, 4, 2, 5, 3, 4, 4, 3, 5, 4, 7, 4, 5, 8, 6, 5, 3, 7, 2, 2, 8, 7,... A majority of numbers of the sequence are even, except 1, 15, 315, 351, 357, 2871, 3663,... Replacing the function lambda(n) by the Euler totient function phi(n) (A000010) gives only the short sequence {1, 2, 6} for n < 10^7. LINKS Amiram Eldar, Table of n, a(n) for n = 1..10000 EXAMPLE 6 is in the sequence because the divisors of 6 are {1,2,3,6} => 1/lambda(1)+1/lambda(2)+1/lambda(3)+ 1/lambda(6) = 1/1 + 1/1 + 1/2 + 1/2 = 3 is an integer. MATHEMATICA lst={}; Do[If[IntegerQ[Total[1/CarmichaelLambda[Divisors[n]]]], AppendTo[lst, n]], {n, 0, 2500}]; lst CROSSREFS Cf. A000010, A002322. Sequence in context: A282358 A064796 A304483 * A083769 A057656 A247066 Adjacent sequences: A268174 A268175 A268176 * A268178 A268179 A268180 KEYWORD nonn AUTHOR Michel Lagneau, Jan 28 2016 STATUS approved

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Last modified August 10 15:49 EDT 2024. Contains 375056 sequences. (Running on oeis4.)