If (1+x)n=∑r=0n Crxr then 1+C1C01+C2C1⋯1+CnCn−1 is equal to
nn−1(n−1)
(n+1)n−1(n−1)!
(n+1)nn!
(n+1)n+1n!
We have 1+C1C01+C2C1⋯1+CnCn−1
=1+n11+n(n−1)2!n⋯1+1n=(1+n)1⋅(1+n)2⋅(1+n)3…(1+n)n=(n+1)nn!