Calculators are for the lazy II

Let $x=91$ and $y=1$ . Then,

$91^3-3\times91^2+3\times91-1$

$= x^3-3x^2y + 3xy^2 - y^3$

$= (x-y)^3$

Since $x=91$ and $y=1$ ,

$(x-y)^3=90^3=\boxed{729000}$

Let $a=91$ . We have:

$91^3 - 3 \times 91^2 + 3 \times 91 -1\\ =a^3 - 3a^2 + 3a - 1\\ =(a-1)^3\\ =(91-1)^3\\ =90^3 =\boxed{729000}$