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A172207 Number of ways to place 3 nonattacking bishops on a 3 X n board. 4
1, 6, 26, 86, 211, 426, 758, 1234, 1881, 2726, 3796, 5118, 6719, 8626, 10866, 13466, 16453, 19854, 23696, 28006, 32811, 38138, 44014, 50466, 57521, 65206, 73548, 82574, 92311, 102786, 114026, 126058 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

V. Kotesovec, Number of ways of placing non-attacking queens and kings on boards of various sizes

FORMULA

Explicit formula (Vaclav Kotesovec, Jan 26 2010): a(n) = (9n^3-45n^2+106n-108)/2, n>=4.

G.f.: x*(2*x^6+14*x^3+8*x^2+2*x+1)/(x-1)^4. - Vaclav Kotesovec, Mar 25 2010

MATHEMATICA

CoefficientList[Series[(2 x^6 + 14 x^3 + 8 x^2 + 2 x + 1) / (x - 1)^4, {x, 0, 50}], x] (* Vincenzo Librandi, May 27 2013 *)

CROSSREFS

Cf. A172124, A061989, A047659, A061996.

Sequence in context: A094162 A229572 A224035 * A060101 A036422 A166214

Adjacent sequences:  A172204 A172205 A172206 * A172208 A172209 A172210

KEYWORD

nonn,easy

AUTHOR

Vaclav Kotesovec, Jan 29 2010

STATUS

approved

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Last modified June 28 23:40 EDT 2017. Contains 288852 sequences.