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A239208 Numbers n such that sigma(n) divides the sum of the numbers x not coprime to n, with x<=n. 2
18, 135, 891, 4095, 10560, 13120, 14144, 21600, 23199, 74655, 144495, 192311, 404415, 4197375, 4612608, 5675775, 6664680, 9180800, 10953215, 11110400, 14381055, 18162144, 18420480, 18920000, 20765024, 25159680, 32058351, 41055200, 55889920, 65327104, 65982464 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Numbers n such that sigma(n) | n/2(n+1-phi(n)).

LINKS

Giovanni Resta, Table of n, a(n) for n = 1..100

EXAMPLE

18/2*(19-phi(18)) = 117, sigma(18) = 39 and 117 / 39 = 3.

MAPLE

with(numtheory); P:=proc(q) local a, n;

for n from 1 to q do a:=n/2*(n+1-phi(n)); if type(a/sigma(n), integer) then print(n);

fi; od; end: P(10^6);

CROSSREFS

Cf. A000010, A000230, A238232, A239205.

Sequence in context: A022710 A056003 A337002 * A114239 A087115 A163707

Adjacent sequences:  A239205 A239206 A239207 * A239209 A239210 A239211

KEYWORD

nonn,easy

AUTHOR

Paolo P. Lava, Mar 12 2014

EXTENSIONS

a(14)-a(31) from Giovanni Resta, Mar 12 2014

STATUS

approved

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Last modified November 24 06:34 EST 2020. Contains 338607 sequences. (Running on oeis4.)