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A070779
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Expansion of e.g.f.: (exp(x/(1-x))*(2-x)-1+x)/(1-x)^3.
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3
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1, 5, 28, 185, 1426, 12607, 125882, 1401409, 17209234, 231033431, 3365440882, 52855452817, 890097287834, 15996379554079, 305519496498106, 6178746162639617, 131885301216119842, 2962568890205560999, 69853182607494217154, 1724761580035969997521, 44501146220521229674282
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OFFSET
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0,2
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COMMENTS
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Equal to the number of strictly partial permutations on [n]; i.e. equal to the cardinality of the complement I_n\S_n, where I_n and S_n denote the symmetric inverse monoid and symmetric group on [n]. - James East, May 03 2007
Former name was "E.g.f.: (exp(x/(1-x))-1)/(1-x)." However, that would be the e.g.f. with offset 1 rather than 0. - Robert Israel, Jan 03 2019
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LINKS
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FORMULA
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In Maple notation, a(n) = n! *(n+1)^2 *hypergeom([1, -n], [2, 2], -1).
D-finite with recurrence a(n) = (3*n+2)*a(n-1) - 3*n^2*a(n-2) + n*(n-1)^2*a(n-3). - Robert Israel, Jan 03 2019
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MAPLE
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f:= gfun:-rectoproc({(n + 3)*(n + 2)^2*a(n) - 3*(n + 3)^2*a(n + 1) + (3*n + 11)*a(n + 2) - a(n + 3)=0, a(0)=1, a(1)=5, a(2)=28}, a(n), remember):
# alternative
n!*(n+1)^2*hypergeom([1, -n], [2, 2], -1) ;
simplify(%) ;
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MATHEMATICA
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Table[(n + 1)! (LaguerreL[n + 1, -1] -1), {n, 0, 20}] (* Vincenzo Librandi, Jan 04 2019 *)
With[{nn=20}, CoefficientList[Series[(Exp[x/(1-x)](2-x)-1+x)/(1-x)^3, {x, 0, nn}], x] Range[0, nn]!] (* Harvey P. Dale, Sep 07 2020 *)
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PROG
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(Sage)
@cached_function
def a(n):
if n < 3: return [1, 5, 28][n]
return n*(n-1)^2*a(n-3)-3*n^2*a(n-2)+(3*n+2)*a(n-1)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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