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A119242 Least number k such that there are exactly n powerful numbers between k^2 and (k+1)^2. 2
1, 2, 5, 31, 234, 1822, 3611, 17329, 1511067, 524827, 180469424, 472532614, 78102676912 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Pettigrew gives a(1)-a(6) in table 14. He conjectures that k exists for every n. Surprisingly, a(8) is greater than 10^6, but a(9)=524827. The Mathematica program creates all powerful numbers <= nMax by computing all products of the form x^2 y^3.

a(10) is greater than 10^8. - Giovanni Resta, May 11 2006

a(n) > 10^11 for n >= 13. - Donovan Johnson, Sep 03 2013

LINKS

Table of n, a(n) for n=0..12.

Donovan Johnson, Powerful numbers between k^2 and (k+1)^2

Steve Pettigrew, Sur la distribution de nombres speciaux consecutifs, M.Sc. Thesis, Univ. Laval, 2000.

EXAMPLE

a(3)=31 because 968, 972 and 1000 are between 961 and 1024.

MATHEMATICA

nMax=10^12; lst={}; Do[lst=Join[lst, i^3 Range[Sqrt[nMax/i^3]]^2], {i, nMax^(1/3)}]; lst=Union[lst]; n=0; k=1; Do[n0=k; While[lst[[k]]<j^2, k++ ]; n1=k; If[n1-n0-1==n, Print[{n, j-1}]; n++ ], {j, Sqrt[nMax]}]

CROSSREFS

Cf. A001694.

Sequence in context: A261750 A189559 A077483 * A068145 A032112 A058009

Adjacent sequences:  A119239 A119240 A119241 * A119243 A119244 A119245

KEYWORD

more,nonn

AUTHOR

T. D. Noe, May 09 2006

EXTENSIONS

a(8) and the previously known a(9) from Giovanni Resta, May 11 2006

a(10)-a(11) from Donovan Johnson, Dec 07 2008

a(12) from Donovan Johnson, Sep 01 2013

STATUS

approved

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Last modified July 5 03:37 EDT 2020. Contains 335459 sequences. (Running on oeis4.)