Given the sum, k∑n=1∞∑j=0j∏r=01n+rk I am trying to find an integral approximation, but any other approximation method would also be a good start. The obviously tricky part about this sum is the product it contains, but alas using the Stirling factorial approximation technique (turning the product into a sum with logarithms) has led me nowhere. Any help would be greatly appreciated.
Answer
Term n is
Tn=∞∑j=0j∏r=01n+rk=kn/k−1e1/k(Γ(nk)−Γ(nk,1k))
If you want an integral, you can represent this as
Tn=e1/kk∫10e−t/ktn/k−1dt
For large k, you can approximate e(1−t)/k≈1+(1−t)/k
making this
Tn≈k+n+1n(k+n)
and then your expression
k∑n=1Tn≈ln(k)+γ
No comments:
Post a Comment