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Search: id:A081251
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| A081251 |
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Numbers n such that A081249(m)/m^2 has a local maximum for m = n. |
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+0
4
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| 2, 6, 20, 60, 182, 546, 1640, 4920, 14762, 44286, 132860, 398580, 1195742, 3587226, 10761680, 32285040, 96855122, 290565366, 871696100, 2615088300, 7845264902, 23535794706, 70607384120, 211822152360, 635466457082, 1906399371246
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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The limit of the local maxima, lim A081249(n)/n^2 = 1/6. For local minima cf. A081250.
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LINKS
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K. Brockhaus, Illustration for A081134, A081249, A081250 and A081251
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FORMULA
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a(n) = floor(3^n*9/4).
a(n) = a(n-2) + 2*3^(n) for n > 1; a(n+2) - a(n) = A008776(n); a(n) = 2*A033113(n+1); a(2n+1) = A054880(n+1).
G.f.: 2/((x - 1)*(x + 1)*(3*x - 1)).
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EXAMPLE
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6 is a term since A081249(5)/5^2 = 4/25 = 0.160, A081249(6)/6^2 = 7/36 = 0.194, A081249(7)/7^2 = 9/49 = 0.184.
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MAPLE
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a[0]:=0:a[1]:=2:for n from 2 to 50 do a[n]:=2*a[n-1]+3*a[n-2]+2 od: seq(a[n], n=1..26); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Apr 28 2008
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CROSSREFS
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Cf. A081134, A081249, A081250, A008776, A033113, A054880.
Adjacent sequences: A081248 A081249 A081250 this_sequence A081252 A081253 A081254
Sequence in context: A082045 A005628 A000620 this_sequence A134293 A136883 A057766
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KEYWORD
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nonn
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AUTHOR
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Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), Mar 17 2003
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