#17161: Implement the unsigned Lah numbers
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Reporter: pluschny | Owner:
Type: enhancement | Status: new
Priority: minor | Milestone: sage-6.4
Component: combinatorics | Resolution:
Keywords: Lah numbers | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Comment (by pluschny):
A possible implementation could be based on:
{{{
def lah_number(n, k):
if n == k: return 1
if n<0 and k<0: return lah_number(-k, -n)
if k<0 or k>n: return 0
return (k*n*gamma(n)^2)/(gamma(k+1)^2*gamma(n-k+1))
}}}
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Ticket URL: <http://trac.sagemath.org/ticket/17161#comment:1>
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