∑ni=16i2=an3+bn2+cn+d. Then
a = 2
b = 3
c = 2
d = 5
∑ni=16i2
=6∑ni=1i2
=6n6(n+1)(2n+1)
=n(2n2+3n+1)
=2n3+3n2+n
∑ni=16i2=an3+bn2+cn+dn.Then d =