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A111177
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Number of base n numbers in which each digit appears at most once (all unnecessary 0's deleted).
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0
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4, 21, 130, 913, 7176, 62629, 602806, 6356865, 72994348, 907497301, 12152572554, 174476220241, 2674434002800, 43603430324133, 753581024080126, 13763517571878529, 264919276238885076, 5360264479811601685
(list; graph; refs; listen; history; internal format)
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OFFSET
| 2,1
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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).
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LINKS
| Cf. A001339.
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FORMULA
| a(n)=Sum(i=0, n-1) (i^2+i+1)(n-1)!/(n-1-i)!; n>1
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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).
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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 *)
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CROSSREFS
| Sequence in context: A032326 A007345 A099250 * A141052 A058308 A078591
Adjacent sequences: A111174 A111175 A111176 * A111178 A111179 A111180
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KEYWORD
| nonn,base
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AUTHOR
| Rafael Hofman (mathematics287(AT)yahoo.de), Oct 22 2005
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EXTENSIONS
| More terms from Robert G. Wilson v (rgwv(at)rgwv.com), Oct 29 2005
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