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A015221
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Odd square pyramidal numbers.
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0
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1, 5, 55, 91, 285, 385, 819, 1015, 1785, 2109, 3311, 3795, 5525, 6201, 8555, 9455, 12529, 13685, 17575, 19019, 23821, 25585, 31395, 33511, 40425, 42925, 51039, 53955, 63365, 66729, 77531, 81375, 93665, 98021, 111895, 116795, 132349, 137825
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OFFSET
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0,2
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LINKS
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Table of n, a(n) for n=0..37.
Index to sequences with linear recurrences with constant coefficients, signature (1,3,-3,-3,3,1,-1)
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FORMULA
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Odd numbers in A000330.
Contribution from Ant King, Oct 17 2012: (Start)
a(n) = 3*a(n-2)-3*a(n-4)+a(n-6)+128.
a(n) = 1/24*(1+4*n+(-1)^n)*(2+4*n+(-1)^n)*(3+4*n+(-1)^n).
G. f. (1+4*x+47*x^2+24*x^3+47*x^4+4*x^5+x^6)/((1-x)^4*(1+x)^3).
(End)
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MATHEMATICA
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LinearRecurrence[{1, 3, -3, -3, 3, 1, -1}, {1, 5, 55, 91, 285, 385, 819}, 38] (* Ant King Oct 17 2012 *)
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CROSSREFS
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Sequence in context: A085719 A129420 A216446 * A035305 A057722 A078216
Adjacent sequences: A015218 A015219 A015220 * A015222 A015223 A015224
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KEYWORD
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nonn,easy
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AUTHOR
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Mohammad K. Azarian
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EXTENSIONS
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More terms from Erich Friedman.
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STATUS
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approved
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