PhpSpreadsheet/tests/data/ColumnIndex.php

<?php

return [
    [
        'A',
        0,
    ],
    [
        'Z',
        25,
    ],
    [
        'AA',
        26,
    ],
    [
        'AB',
        27,
    ],
    [
        'AZ',
        51,
    ],
    [
        'BA',
        52,
    ],
    [
        'BZ',
        77,
    ],
    [
        'CA',
        78,
    ],
    [
        'IV',
        255,
    ],
    [
        'ZZ',
        701,
    ],
    [
        'AAA',
        702,
    ],
    [
        'BAA',
        1378,
    ],
];