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A172529 Number of ways to place 2 nonattacking knights on an n X n toroidal board. 7
0, 2, 18, 88, 200, 486, 980, 1760, 2916, 4550, 6776, 9720, 13520, 18326, 24300, 31616, 40460, 51030, 63536, 78200, 95256, 114950, 137540, 163296, 192500, 225446, 262440, 303800, 349856, 400950, 457436, 519680, 588060, 662966, 744800, 833976, 930920, 1036070 (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

a(n) = n^2*(n+3)*(n-3)/2, n>=5.

G.f.: 2*x^2*(16*x^7-71*x^6+121*x^5-98*x^4+40*x^3-9*x^2-4*x-1)/(x-1)^5. - Vaclav Kotesovec, Mar 25 2010

MATHEMATICA

CoefficientList[Series[2 x (16 x^7 - 71 x^6 + 121 x^5 - 98 x^4 + 40 x^3 - 9 x^2 - 4 x - 1) / (x - 1)^5, {x, 0, 50}], x] ( * Vincenzo Librandi, May 29 2013 *)

CROSSREFS

Cf. A172132, A172517.

Sequence in context: A091940 A068605 A070171 * A201236 A206623 A036800

Adjacent sequences:  A172526 A172527 A172528 * A172530 A172531 A172532

KEYWORD

nonn,easy

AUTHOR

Vaclav Kotesovec, Feb 06 2010

EXTENSIONS

More terms from Vincenzo Librandi, May 29 2013

STATUS

approved

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Last modified December 18 20:06 EST 2018. Contains 318245 sequences. (Running on oeis4.)