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A038522
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On a (2n+1) X (2n+1) board, let m(i) be the number of squares that are i knight's moves from center; sequence gives max m(i) for i >= 0.
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2
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1, 1, 8, 20, 32, 52, 68, 76, 96, 96, 120, 120, 148, 148, 176, 176, 204, 204, 232, 232, 260, 260, 288, 288, 316, 316, 344, 344, 372, 372, 400, 400, 428, 428, 456, 456, 484, 484, 512, 512, 540, 540, 568, 568, 596, 596, 624, 624, 652, 652, 680, 680, 708, 708
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OFFSET
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0,3
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LINKS
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Andreas P. Hadjipolakis, Problem E2605, Am. Math. Monthly Vol. 83 (1976), no. 7 (Aug-Sept.), p. 566.
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FORMULA
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G.f.: (1 + 6*x^2 + 12*x^3 + 5*x^4 + 8*x^5 + 4*x^6 - 12*x^7 + 4*x^8 - 8*x^9 + 4*x^10 + 4*x^12)/((1 - x)^2*(1 + x)).
a(n) = a(n-1) + a(n-2) - a(n-3) for n > 12. (End)
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EXAMPLE
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On a 5 X 5 board, [ m(0),...,m(4) ]=[ 1,8,8,4,4 ], max=8, so a(2)=8.
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MATHEMATICA
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LinearRecurrence[{1, 1, -1}, {1, 1, 8, 20, 32, 52, 68, 76, 96, 96, 120, 120, 148}, 60] (* Harvey P. Dale, Apr 15 2020 *)
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PROG
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(PARI) Vec((1 + x^2)*(1 + 5*x^2 + 12*x^3 - 4*x^5 + 4*x^6 - 8*x^7 + 4*x^10) / ((1 - x)^2*(1 + x)) + O(x^50)) \\ Colin Barker, Mar 16 2020
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CROSSREFS
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KEYWORD
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easy,nonn,walk,nice
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AUTHOR
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Antreas P. Hatzipolakis (xpolakis(AT)hol.gr)
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EXTENSIONS
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STATUS
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approved
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