0,2

For n>=2, a(n) is equal to the number of functions f:{1,2,...,n}->{1,2,3,4,5,6,7,8,9,10,11} such that for fixed, different x_1, x_2 in {1,2,...,n} and fixed y_1, y_2 in {1,2,3,4,5,6,7,8,9,10,11} we have f(x_1)<>y_1 and f(x_2)<> y_2. - Milan R. Janjic (agnus(AT)blic.net), Apr 19 2007

A. H. Beiler, Recreations in the Theory of Numbers, Dover, N.Y., 1964, pps. 194-196.

Milan Janjic, Enumerative Formulas for Some Functions on Finite Sets

a(n)=11a(n-1)+[(-1)^n]*C(2, 2-n). G.f.(x)=(1-x)^2/(1-11x).

Cf. A001020.

Sequence in context: A027769 A065736 A092936 this_sequence A060150 A103461 A101563

Adjacent sequences: A055999 A056000 A056001 this_sequence A056003 A056004 A056005

easy,nonn

Barry E. Williams, Jun 18 2000

More terms from James A. Sellers (sellersj(AT)math.psu.edu), Jul 04 2000