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 A111177 Number of base n numbers in which each digit appears at most once (all unnecessary 0's deleted). 0
 4, 21, 130, 913, 7176, 62629, 602806, 6356865, 72994348, 907497301, 12152572554, 174476220241, 2674434002800, 43603430324133, 753581024080126, 13763517571878529, 264919276238885076, 5360264479811601685 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,1 COMMENTS Finite expansions after the "decimal" point are allowed, but there must be a number before it (so we can have 0.1, but not .01). LINKS Table of n, a(n) for n=2..19. Cf. A001339. FORMULA a(n)=Sum(i=0, n-1) (i^2+i+1)(n-1)!/(n-1-i)!; n>1 EXAMPLE a(2)=4 because in the binary system only the numbers 0; 1; 0.1; 10 can be written with each digit used at most once (all unnecessary 0's deleted). MATHEMATICA f[n_] := Sum[(i^2 + i + 1)(n - 1)!/(n - 1 - i)!, {i, 0, n - 1}]; Table[ f[n], {n, 2, 19}] (* Robert G. Wilson v *) CROSSREFS Sequence in context: A300674 A232956 A234268 * A141052 A058308 A078591 Adjacent sequences: A111174 A111175 A111176 * A111178 A111179 A111180 KEYWORD nonn,base AUTHOR Rafael Hofman (mathematics287(AT)yahoo.de), Oct 22 2005 EXTENSIONS More terms from Robert G. Wilson v, Oct 29 2005 STATUS approved

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Last modified December 11 02:45 EST 2023. Contains 367717 sequences. (Running on oeis4.)