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A056106
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Second spoke of a hexagonal spiral.
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24
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1, 3, 11, 25, 45, 71, 103, 141, 185, 235, 291, 353, 421, 495, 575, 661, 753, 851, 955, 1065, 1181, 1303, 1431, 1565, 1705, 1851, 2003, 2161, 2325, 2495, 2671, 2853, 3041, 3235, 3435, 3641, 3853, 4071, 4295, 4525, 4761, 5003, 5251, 5505, 5765, 6031, 6303
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refs;
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history;
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OFFSET
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0,2
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COMMENTS
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First differences of A027444. - J. M. Bergot, Jun 04 2012
Numbers of the form ((h^2+h+1)^2+(-h^2+h+1)^2+(h^2+h-1)^2)/(h^2-h+1) for h=n-1. - Bruno Berselli, Mar 13 2013
For n > 0: 2*a(n) = A058331(n) + A001105(n) + A001844(n-1) = A251599(3*n-2) + A251599(3*n-1) + A251599(3*n). - Reinhard Zumkeller, Dec 13 2014
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LINKS
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Vincenzo Librandi, Table of n, a(n) for n = 0..10000
H. Bottomley, Spokes of a hexagonal spiral (illustration of initial terms).
G. Nebe and N. J. A. Sloane, Home page for hexagonal (or triangular) lattice A2.
Index entries for linear recurrences with constant coefficients, signature (3,-3,1).
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FORMULA
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a(n) = 3*n^2 - n + 1.
a(n) = a(n-1) + 6*n - 4 = 2*a(n-1) - a(n-2) + 6.
a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3).
E.g.f.: (1+2*x+3*x^2)*exp(x). - Paul Barry, Mar 13 2003
a(n) = A096777(3*n) for n>0. - Reinhard Zumkeller, Dec 29 2007
G.f.: (1+5*x^2)/(1-3*x+3*x^2-x^3). - Colin Barker, Jan 04 2012
a(n) = n*A002061(n+1) - (n-1)*A002061(n). - Bruno Berselli, Jan 15 2013
a(-n) = A056108(n). - Bruno Berselli, Mar 13 2013
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MATHEMATICA
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Table[3*n^2 - n + 1, {n, 0, 50}] (* G. C. Greubel, Jul 19 2017 *)
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PROG
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(MAGMA) I:=[1, 3]; [n le 2 select I[n] else 2*Self(n-1)-Self(n-2)+6: n in [1..50]]; // Vincenzo Librandi, Nov 14 2011
(PARI) a(n) = 3*n^2-n+1;
(Haskell)
a056106 n = n * (3 * n - 1) + 1 -- Reinhard Zumkeller, Dec 13 2014
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CROSSREFS
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Cf. A054552 for example of square (or octagonal) spiral spoke.
Cf. A002061.
Cf. A001105, A001844, A058331, A251599.
Sequence in context: A185258 A118436 A293413 * A320035 A147382 A212971
Adjacent sequences: A056103 A056104 A056105 * A056107 A056108 A056109
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KEYWORD
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nonn,easy
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AUTHOR
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Henry Bottomley, Jun 09 2000
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STATUS
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approved
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