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A036907 Square refactorable numbers. 4

%I

%S 1,9,36,225,441,625,1089,1521,2025,2601,3249,3600,4761,5625,6561,7569,

%T 8100,8649,10000,12321,15129,16641,19881,22500,25281,26244,28224,

%U 31329,32400,33489,35721,40401,45369,47961,50625,56169,62001,71289,84681

%N Square refactorable numbers.

%H Harvey P. Dale, <a href="/A036907/b036907.txt">Table of n, a(n) for n = 1..1000</a>

%H S. Colton, <a href="http://www.cs.uwaterloo.ca/journals/JIS/colton/joisol.html">Refactorable Numbers - A Machine Invention</a>, J. Integer Sequences, Vol. 2, 1999, #2.

%H S. Colton, <a href="http://web.archive.org/web/20070831060523/http://www.dai.ed.ac.uk/homes/simonco/research/hr/">HR - Automatic Theory Formation in Pure Mathematics</a>

%e 9 is refactorable because tau(9)=3 and 3 divides 9 and 9 is a square number.

%t Select[Range[300]^2,Divisible[#,DivisorSigma[0,#]]&] (* _Harvey P. Dale_, Nov 21 2020 *)

%o (PARI) isok(n) = issquare(n) && ! (n % numdiv(n)); \\ _Michel Marcus_, Aug 31 2013

%Y A033950.

%K nonn

%O 1,2

%A Simon Colton (simonco(AT)cs.york.ac.uk)

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Last modified August 17 23:13 EDT 2022. Contains 356204 sequences. (Running on oeis4.)