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A computer algebra system written in pure Python
https://sympy.org/
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wrong Sum(binomial(n, k)*(n - k)**4*(-1)**k, (k,0,n)) #8077

Open pernici opened 10 years ago

pernici commented 10 years ago 
>>> from sympy import *
>>> n = symbols('n', integer=True, positive=True)
>>> k = symbols('k', integer=True)
>>> Sum(binomial(n, k)*(n - k)**4*(-1)**k, (k,0,n)).doit()
0

This is wrong for n <= 4

pelegm commented 9 years ago

Similarly,

Sum(binomial(n, k)*(n - k)**2*(-1)**k, (k,0,n)).doit()

returns 0, which is wrong for n <= 2.