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A168493
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a(n) = 3^floor(n^2/2).
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2
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1, 1, 9, 81, 6561, 531441, 387420489, 282429536481, 1853020188851841, 12157665459056928801, 717897987691852588770249, 42391158275216203514294433201, 22528399544939174411840147874772641, 11972515182562019788602740026717047105681
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OFFSET
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0,3
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COMMENTS
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Hankel transform of A168492. A trivial Somos-4 sequence linked to elliptic curve y^2 = 1 - 16x + 76x^2 - 96x^3.
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LINKS
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G. C. Greubel, Table of n, a(n) for n = 0..50
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FORMULA
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a(n) = 3^floor(n^2/2) = 9^floor(n^2/4) = 9^A002620(n) = 81*a(n-2)^2/a(n-4).
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MATHEMATICA
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Table[3^Floor[n^2/2], {n, 0, 20}] (* Harvey P. Dale, Mar 06 2011 *)
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PROG
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(MAGMA) [3^Floor(n^2/2): n in [0..15]]; // Vincenzo Librandi, Jul 24 2016
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CROSSREFS
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Sequence in context: A344402 A167723 A203107 * A003302 A053915 A067216
Adjacent sequences: A168490 A168491 A168492 * A168494 A168495 A168496
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KEYWORD
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easy,nonn
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AUTHOR
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Paul Barry, Nov 27 2009
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STATUS
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approved
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