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 A201244 Number of ways to place 3 non-attacking ferses on an n X n board. 7
 0, 0, 38, 340, 1630, 5552, 15210, 35828, 75530, 146240, 264702, 453620, 742918, 1171120, 1786850, 2650452, 3835730, 5431808, 7545110, 10301460, 13848302, 18357040, 24025498, 31080500, 39780570, 50418752, 63325550, 78871988, 97472790, 119589680, 145734802 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Fers is a leaper [1,1]. LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..1000 V. Kotesovec, Non-attacking chess pieces, 6ed, p.415 Index entries for linear recurrences with constant coefficients, signature (7,-21,35,-35,21,-7,1). FORMULA a(n) = (n-2)*(n^5 + 2n^4 - 11n^3 + 2n^2 + 54n - 60)/6, n>=2. G.f.: -2x^3*(x^5 + 3x^4 - 24x^3 + 24x^2 + 37x + 19)/(x-1)^7. a(n) = 7*a(n-1)-21*a(n-2)+35*a(n-3)-35*a(n-4)+21*a(n-5)-7*a(n-6)+a(n-7). - Vincenzo Librandi, Apr 30 2013 MATHEMATICA CoefficientList[Series[- 2 x^2 (x^5 + 3 x^4 - 24 x^3 + 24 x^2 + 37 x + 19) / (x-1)^7, {x, 0, 40}], x] (* Vincenzo Librandi, Apr 30 2013 *) PROG (MAGMA) I:=[0, 0, 38, 340, 1630, 5552, 15210, 35828]; [n le 8 select I[n] else 7*Self(n-1)-21*Self(n-2)+35*Self(n-3)-35*Self(n-4)+21*Self(n-5)-7*Self(n-6)+Self(n-7): n in [1..40]]; /* or */ [0] cat [(n-2)*(n^5+2*n^4-11*n^3 +2*n^2+54*n-60)/6: n in [2..35]]; // Vincenzo Librandi, Apr 30 2013 CROSSREFS Cf. A172124, A201243, A201245, A201246, A201247, A201248. Sequence in context: A297799 A204070 A242209 * A240263 A156661 A249711 Adjacent sequences:  A201241 A201242 A201243 * A201245 A201246 A201247 KEYWORD nonn,easy AUTHOR Vaclav Kotesovec, Nov 28 2011 STATUS approved

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Last modified January 18 10:47 EST 2022. Contains 350454 sequences. (Running on oeis4.)