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A036458
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For all n, if d is recursively applied to a(n) exactly 6 times then the fixed point of d-iteration is just reached.
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2
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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, 20592, 20880, 21060, 21168
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OFFSET
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1,1
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COMMENTS
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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
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LINKS
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FORMULA
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EXAMPLE
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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 iterations the convergence takes place through 72,12,6,4,3 transients, i.e., 2 is reached on the 6th step.
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MATHEMATICA
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draQ[n_]:=Length[FixedPointList[DivisorSigma[0, #]&, n, 7]]==8; Select[ Range[ 21000], draQ] (* Harvey P. Dale, Mar 06 2015 *)
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PROG
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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