Project Euler - Problem #28

number-spiral.txt

21 22 23 24 25
20  7  8  9 10
19  6  1  2 11
18  5  4  3 12
17 16 15 14 13

solution.php

$total = 1;
for ($i = 2; $i <= 1001; $i++) {
    $total += ($i % 2) ? pow($i, 2) : 3 _ pow($i, 2) + 3;
}
echo $total;