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A204503
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Squares n^2 such that floor(n^2/9) is again a square.
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20
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0, 1, 4, 9, 16, 36, 81, 144, 225, 324, 441, 576, 729, 900, 1089, 1296, 1521, 1764, 2025, 2304, 2601, 2916, 3249, 3600, 3969, 4356, 4761, 5184, 5625, 6084, 6561, 7056, 7569, 8100, 8649, 9216, 9801, 10404, 11025, 11664, 12321, 12996, 13689, 14400, 15129, 15876
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OFFSET
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1,3
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COMMENTS
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Or: Squares which remain squares when their last base-9 digit is dropped.
(For the first three terms, which have only 1 digit in base 9, dropping that digit is meant to yield zero.)
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LINKS
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FORMULA
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Conjectures: a(n) = 9*(n-4)^2 for n>5. G.f.: x^2*(7*x^6-12*x^5-11*x^4-x-1) / (x-1)^3. - Colin Barker, Sep 15 2014
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MATHEMATICA
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Select[Range[0, 200]^2, IntegerQ[Sqrt[Floor[#/9]]]&] (* Harvey P. Dale, Jan 27 2012 *)
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PROG
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(PARI) b=9; for(n=1, 200, issquare(n^2\b) & print1(n^2, ", "))
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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