login
A272501
Number of n-letter strings over a ten letter alphabet where no letter appears exactly three times.
3
1, 10, 100, 990, 9640, 91900, 855100, 7754050, 68545360, 592095160, 5020469200, 42054532750, 350538754600, 2926602465940, 24587635740040, 208406304739450, 1784567064858400, 15453880256710000, 135459380264937760, 1202295227210127910, 10804306958861721400
OFFSET
0,2
COMMENTS
species is SEQ_10(SET_(!=3)(Z))
FORMULA
E.g.f.: (exp(z)-z^3/3!)^10.
EXAMPLE
a(3) = 10^3-10 because all 3-letter strings qualify except the strings containing only one type of letter.
MAPLE
a := n->n!*coeftayl((exp(z)-z^3/3!)^10, z=0, n);
MATHEMATICA
With[{nn=20}, CoefficientList[Series[(Exp[x]-x^3/3!)^10, {x, 0, nn}], x] Range[ 0, nn]!] (* Harvey P. Dale, Apr 08 2019 *)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Marko Riedel, May 01 2016
STATUS
approved