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A036458 For all n, if d recursively applied to a(n) exactly 6 times then the fixed point of d-iteration is just reached. 2
5040, 7920, 8400, 9360, 10080, 10800, 11088, 11340, 11760, 12240, 12600, 12960, 13104, 13200, 13680, 13860, 15600, 15840, 16200, 16380, 16560, 16800, 17136, 17640, 17820, 18000, 18144, 18720, 18900, 19152, 19440, 19800, 20160, 20400 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Observe that the values giving stationary value in 6 steps are rather large.

"d" in the definition refers to the number of divisors of n. - Harvey P. Dale, Mar 06 2015

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

FORMULA

A036459(a(n)) = 6. - Ivan Neretin, Jan 25 2016

EXAMPLE

a(1)=5040 and the nested d functions are 60,12,6,4,3 and the 6th is 2. a(5)=10080 and iterating d with 10080 initial value, after 6 iteration the convergence takes place through 72,12,6,3 transients, i.e. 2 is reached on the 6th step.

MATHEMATICA

draQ[n_]:=Length[FixedPointList[DivisorSigma[0, #]&, n, 7]]==8; Select[ Range[ 21000], draQ] (* Harvey P. Dale, Mar 06 2015 *)

PROG

(PARI) is(n)=for(i=1, 5, n=numdiv(n); if(n<3, return(0))); numdiv(n)==2 \\ Charles R Greathouse IV, Sep 17 2015

CROSSREFS

Cf. A036457.

Sequence in context: A269125 A111030 A068378 * A190107 A090393 A147632

Adjacent sequences:  A036455 A036456 A036457 * A036459 A036460 A036461

KEYWORD

nonn

AUTHOR

Labos Elemer

STATUS

approved

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Last modified June 7 02:48 EDT 2020. Contains 334836 sequences. (Running on oeis4.)