December 2020
w| Mo Tu We Th Fr Sa Su
49| 1 2 3 4 5 6
50| 7 8 9 10 11 12 13
51| 14 15 16 17 18 19 20
52| 21 22 23 24 25 26 27
*53| 28 29 30 31 *
January 2021
w| Mo Tu We Th Fr Sa Su
*53| 1 2 3*
1| 4 5 6 7 8 9 10
2| 11 12 13 14 15 16 17
3| 18 19 20 21 22 23 24
4| 25 26 27 28 29 30 31
<?php
$date = new DateTimeImmutable("2021-01-02");
echo $date->format('o-\WW-\DN');
?>