Find an expression for the sum of the series

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SUMMARY

The discussion focuses on deriving an expression for the sum of the series defined as (1x2x6) + (2x3x7) + ... + n(n + 1)(n + 5). The solution involves recognizing that the sum can be represented as a polynomial of degree four, specifically S = a*n^4 + b*n^3 + c*n^2 + d*n + e. By substituting values for n from 1 to 5, participants can create a system of five equations to solve for the coefficients a, b, c, d, and e, thereby determining the polynomial expression for the series.

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Homework Statement



(1x2x6) + (2x3x7) + ... + n(n + 1)(n + 5)



Homework Equations



Find an expression for the sum of the series. Give your answer as a product of linear factors in n.


The Attempt at a Solution



I haven't tried it since I don't know what to do.
 
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I haven't seen one of those for years! They are interesting. There is some theory saying that the sum is equal to a polynomial with one degree higher than the term. Your terms are 3rd degree, so you need a 4th degree polynomial:
S = a*n^4 + b*n^3 + c*n^2 + d*n + e
By hand you figure out the sum and the powers for n = 1, 2, 3, 4, and 5.
That gives you a system of 5 equations with 5 unknowns a, b, c, d, e.
Solve the system to get the unknown coefficients.
 

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