If (1+x+x2+⋅⋅+xn)n =a0+a1x+a2x2+⋅⋅⋅+ampxmp then a1+2a2+3a3+⋅⋅⋅+npanp=_______
(1+x+x2+...+xp)n=a0+a1x+...+apnxpn
Differentiating wrt x
⇒n(1+x+x2+...+xp)n−1×(1+2x+3x2+...+pxp−1)=a1+2a2x+...+pnapnxpn−1
Put x=1
⇒n(p+1)n−1p(p+1)2=a1+2a2+...+apn
=np2(p+1)n