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A276734 Numbers n such that the number of divisors of n equals the integer part of the geometric mean of the divisors of n. 1
1, 5, 7, 9, 21, 22, 44, 45, 66, 70, 78, 112, 150, 156, 160, 264, 270, 280, 432, 600, 1080, 1680 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Numbers n such that A000005(n) = floor(A007955(n)^(1/A000005(n))).

Numbers n such that A000005(n) = A000196(n).

Numbers n such that number of divisors of n equals number of squares <= n.

It is assumed that sequence is finite.

Numbers n such that A000196(n)/A000005(n) = r ; r is a rational number. This sequence has r = 1. Does an r exist for which the sequence is infinite ? [Ctibor O. Zizka, Jan 01 2017]

LINKS

Table of n, a(n) for n=1..22.

Ilya Gutkovskiy, Illustration of dynamics of floor(sqrt(n)) - sigma_0(n)

EXAMPLE

a(10) = 70, because 70 has 8 divisors {1, 2, 5, 7, 10, 14, 35, 70} and floor((1*2*5*7*10*14*35*70)^(1/8)) = floor(sqrt(70)) = 8, or equivalent formulation, we have 8 squares {1, 4, 9, 16, 25, 36, 49, 64} <= 70.

MATHEMATICA

Select[Range[10000], DivisorSigma[0, #1] == Floor[Sqrt[#1]] & ]

CROSSREFS

Cf. A000005, A000196, A007955.

Sequence in context: A024571 A186406 A068332 * A268410 A029650 A049307

Adjacent sequences:  A276731 A276732 A276733 * A276735 A276736 A276737

KEYWORD

nonn,more

AUTHOR

Ilya Gutkovskiy, Oct 03 2016

STATUS

approved

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Last modified February 25 20:48 EST 2018. Contains 299656 sequences. (Running on oeis4.)