%Plain TeX -> abstract for V4(2) R21
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\noindent {\bf  Marko Petkov\v sek
and Herbert S. Wilf  }
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When can the sum of $(1/p)$th of the binomial
 coefficients have closed form?
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We find all nonnegative integer 
$r,s,p$ for which the sum 
$\sum_{k=rn}^{sn}{pn\choose k}$ has closed form.
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