Problem 157

Since $(1+x)(2-x)^{6}=[(x-1)+2](1-x+1)^{6}=[(x-1)+2][(x-1)-1]^{6}$,
we can expand it as $[(x-1)+2][\binom{6}{0}(x-1)^{6}-\binom{6}{1}(x-1)^{5}+\binom{6}{2}(x-1)^{4}-\binom{6}{3}(x-1)^{3}+\binom{6}{4}(x-1)^{2}-\binom{6}{5}(x-1)+\binom{6}{6}]$,
and given $$(1+x)(2-x)^{6}=a_{0}+a_{1}(x-1)+a_{2}(x-1)^{2}+\ldots+a_{7}(x-1)^{7}$$,
thus, $a_{3}=-2\binom{6}{3}+\binom{6}{4}=-25$,
so the answer is $\boxed{-25}$.
By transforming the left side of the equation into $[(x-1)+2][(x-1)-1]^{6}$ and then expanding it according to the binomial theorem, we can find the coefficient of $(x-1)^{3}$, which is the value of $a_{3}$.
This problem mainly examines the application of the binomial theorem and the general formula for the expansion of a binomial series, and is considered a medium-level question.