# Sum to infinity (3)

$1 + 4x + 10 x^2 + 20 x^3 + 35 x^4 + 56 x^5 + 84 x^6 + 120 x^7 + \cdots$

Given that the $$n^{\text{th}}$$ term after 1 in the sum above is of the form

$\dfrac{4 \cdot 5 \cdot 6 \cdots ( 4 + (n-1) )}{n!} x^n.$

Evaluate the sum at $$x= \dfrac 23$$.

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