Question 71
Determine all integers which can be expressed in the form
$$
x_1x_2 + x_2x_3 + \dots + x_{k-1}x_k,
$$
where $x_1, x_2, \dots, x_k$ are positive integers whose sum equals $2019$.
$$
x_1x_2 + x_2x_3 + \dots + x_{k-1}x_k,
$$
where $x_1, x_2, \dots, x_k$ are positive integers whose sum equals $2019$.