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 A056120 a(n) = (3^3)*4^(n-3); a(0)=1, a(1)=1. 1
 1, 1, 7, 27, 108, 432, 1728, 6912, 27648, 110592, 442368, 1769472, 7077888, 28311552, 113246208, 452984832, 1811939328, 7247757312, 28991029248, 115964116992, 463856467968, 1855425871872 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS For n>=3, a(n) is equal to the number of functions f:{1,2,...,n}->{1,2,3,4} such that for fixed, different x_1, x_2, x_3 in {1,2,...,n} and fixed y_1, y_2, y_3 in {1,2,3,4} we have f(x_i)<>y_i, (i=1,2,...,n). - Milan Janjic, May 13 2007 LINKS Milan Janjic, Enumerative Formulas for Some Functions on Finite Sets Index entries for linear recurrences with constant coefficients, signature (4). FORMULA a(n)=4a(n-1)+[(-1)^n]*C(3, 3-n). G.f.(x)=(1-x)^3/(1-4x). CROSSREFS Cf. A055841. First differences of A002063. Sequence in context: A054485 A090856 A055917 * A255278 A294262 A048711 Adjacent sequences:  A056117 A056118 A056119 * A056121 A056122 A056123 KEYWORD easy,nonn AUTHOR Barry E. Williams, Jul 05 2000 EXTENSIONS a(21) corrected by R. J. Mathar, Dec 03 2014 STATUS approved

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Last modified February 15 20:32 EST 2019. Contains 320138 sequences. (Running on oeis4.)