Using Closed-Form Formulas

function SquareOfSum(number : longint) : longint;
var
  s : longint;
begin
  s := number * (number + 1) div 2;
  result := s * s;
end;

function SumOfSquares(number : longint) : longint;
begin
  result := number * (number + 1) * (2 * number + 1) div 6;
end;

function DifferenceOfSquares(number : longint) : longint;
begin
  result := SquareOfSum(number) - SumOfSquares(number);
end;

Both functions use closed-form mathematical formulas:

• The sum of integers 1 through n is n * (n + 1) / 2. Squaring that sum gives SquareOfSum.
• The sum of squares of integers 1 through n is n * (n + 1) * (2n + 1) / 6.

These are O(1) operations regardless of the value of number, compared to O(n) for the loop-based approach.

Pascal's div operator performs integer division, truncating any remainder — equivalent to // in Python or integer / in Java. Using div here is correct because both formulas are guaranteed to produce whole-number results: n * (n + 1) is always divisible by 2, and n * (n + 1) * (2n + 1) is always divisible by 6.

Do not use / for integer division in Pascal: when applied to integer operands it produces a real (floating-point) result, which cannot be assigned back to a longint without an explicit cast.

A local variable s is used in SquareOfSum to compute the intermediate sum before squaring, avoiding the need to evaluate the formula twice. SumOfSquares needs no intermediate variable because its result is a single expression.