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A073568 Number of anti-divisors of n divides the number of divisors of n. 1
3, 4, 5, 6, 8, 12, 20, 24, 32, 40, 44, 50, 60, 72, 80, 84, 96, 144, 156, 162, 180, 192, 208, 224, 240, 244, 272, 288, 312, 316, 336, 396, 404, 420, 432, 464, 480, 512, 516, 524, 596, 624, 648, 684, 704, 736, 804 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

See A066272 for definition of anti-divisor.

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

MATHEMATICA

atQ[n_] := Divisible[DivisorSigma[0, n], Count[Flatten[Quotient[#, Rest[Select[Divisors[#], OddQ]]] & /@ (2 n + Range[-1, 1])], Except[1]]]; Select[Range[3, 805], atQ] (* Jayanta Basu, Jul 01 2013 *)

PROG

(PARI) ad(n)=numdiv(2*n+1)+numdiv(2*n-1)+numdiv(n>>valuation(n, 2))-5

is(n)=n>2 && numdiv(n)%ad(n)==0 \\ Charles R Greathouse IV, Jul 01 2013

CROSSREFS

Cf. A066272, A000005.

Sequence in context: A130788 A288819 A087743 * A094576 A103103 A217347

Adjacent sequences:  A073565 A073566 A073567 * A073569 A073570 A073571

KEYWORD

nonn

AUTHOR

Jason Earls, Aug 31 2002

STATUS

approved

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Last modified July 27 06:56 EDT 2021. Contains 346304 sequences. (Running on oeis4.)