- var_dump: documentation ( source)
- array_keys: documentation ( source)
<?php
$promocoesDinamicas = [
1618 => 'BlackFridayDinamica/18: MilkShake P SP',
1619 => 'BlackFridayDinamica/18: 2 MilkShake M SP',
1620 => 'BlackFridayDinamica/18: Big Bob M SP',
1621 => 'BlackFridayDinamica/18: Cheddar M SP',
1622 => 'BlackFridayDinamica/18: Trio Cheddar M SP',
1623 => 'BlackFridayDinamica/18: Bob\'s Twister SP',
1624 => 'BlackFridayDinamica/18: Trio Big Bob Picanha P SP',
];
$keys = array_keys($promocoesDinamicas);
$mod = (6 % count($keys))+1;
$id = (int)350417 % $mod;
var_dump($keys, $mod, $id);