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A023883 Not a prime and average of divisors is an integer. 6
1, 6, 14, 15, 20, 21, 22, 27, 30, 33, 35, 38, 39, 42, 44, 45, 46, 49, 51, 54, 55, 56, 57, 60, 62, 65, 66, 68, 69, 70, 77, 78, 85, 86, 87, 91, 92, 93, 94, 95, 96, 99, 102, 105, 110, 111, 114, 115, 116, 118, 119, 123, 125, 126, 129, 132, 133, 134, 135, 138 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Composite numbers n such that sigma(n)==0 mod tau(n). [Paolo P. Lava, Jun 11 2013]

LINKS

Paolo P. Lava, Table of n, a(n) for n = 1..1000

MAPLE

with(numtheory); ListA023883:=proc(q) local n;

for n from 1 to q do if not isprime(n) then  if  sigma(n) mod tau(n)=0 then

print(n); fi; fi; od;  end: ListA023883(10^6); # Paolo P. Lava, Jun 11 2013

MATHEMATICA

Select[{Mean[Divisors[#]], #}& /@ Select[Range[140], !PrimeQ[#]&], IntegerQ[#[[1]]]&][[All, 2]] (* Jean-François Alcover, Oct 31 2017 *)

CROSSREFS

A003601.

Sequence in context: A079010 A324814 A015822 * A230873 A192321 A190272

Adjacent sequences:  A023880 A023881 A023882 * A023884 A023885 A023886

KEYWORD

nonn

AUTHOR

Olivier Gérard

STATUS

approved

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Last modified May 21 23:21 EDT 2019. Contains 323467 sequences. (Running on oeis4.)