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Search: id:A027468
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| 0, 9, 27, 54, 90, 135, 189, 252, 324, 405, 495, 594, 702, 819, 945, 1080, 1224, 1377, 1539, 1710, 1890, 2079, 2277, 2484, 2700, 2925, 3159, 3402, 3654, 3915, 4185, 4464, 4752, 5049, 5355, 5670, 5994, 6327, 6669, 7020, 7380, 7749, 8127, 8514, 8910, 9315
(list; graph; listen)
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OFFSET
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0,2
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COMMENT
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Staggered diagonal of triangular spiral in A051682, between (0,1,11) spoke and (0,8,25) spoke. - Paul Barry (pbarry(AT)wit.ie), Mar 15 2003
Number of permutations of n distinct letters (ABCD...) each of which appears thrice with n-2 fixed points. - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Oct 15 2006
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REFERENCES
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Zvonkine D., Counting ramified coverings and intersection theory on Hurwitz spaces II (local structure of Hurwitz spaces and combinatorial results), Moscow Mathematical Journal, vol. 7 (2007), no. 1, 135-162.
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LINKS
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D. Zvonkine, Home Page
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FORMULA
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Numerators of sequence a[ n, n-2 ] in (a[ i, j ])^2 where a[ i, j ] = Binomial(i-1, j-1)/2^(i-1) if j<=i, 0 if j>i
a(n) = (9/2)*n*(n+1).
a(n)=9C(n, 1)+9C(n, 2) (binomial transform of (0, 9, 9, 0, 0, .....)). - Paul Barry (pbarry(AT)wit.ie), Mar 15 2003
G.f.: 9x/(1-x)^3. a(-1-n)=a(n).
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MAPLE
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[seq(9*binomial(n, 2) , n=1..46)]; - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Nov 24 2006
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PROGRAM
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(PARI) a(n)=9*n*(n+1)/2
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CROSSREFS
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Third diagonal of A027465. Cf. A033996, A049598.
Cf. A059072, A059073.
Cf. A028895, A046092, A045943, A002378, A028896, A024966, A033996.
Adjacent sequences: A027465 A027466 A027467 this_sequence A027469 A027470 A027471
Sequence in context: A020306 A069068 A051412 this_sequence A112524 A011923 A029875
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KEYWORD
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nonn,easy
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AUTHOR
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Olivier Gerard (ogerard(AT)ext.jussieu.fr)
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EXTENSIONS
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More terms from Patrick De Geest (pdg(AT)worldofnumbers.com), Oct 15 1999.
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