Problem Statement

Compute the   nth   term of a series,   i.e. the sum of the   n   first terms of the corresponding sequence.
Informally this value, or its limit when   n   tends to infinity, is also called the sum of the series, thus the title of this task. For this task, use:

This approximates the   zeta function   for   S=2,   whose exact value is the solution of the Basel problem.

Let's start with the solution:

real
Invsqr(real n)
{
    1 / (n * n);
}

integer
main(void)
{
    integer i;
    real sum;

    sum = 0;

    i = 1;
    while (i < 1000) {
        sum += Invsqr(i);
        i += 1;
    }

    o_real(14, sum);
    o_byte('\n');

    0;
}