A073568 Number of anti-divisors of n divides the number of divisors of n.

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

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