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<?php $arr = [ 0 => "556878", 1 => "12345", 2 => "12345", 3 => "234567", 4 => "45673", 5 => "45673", ]; $n = 2; $result = array_keys(array_intersect(array_count_values($arr), [$n])); var_dump($result);
Output for 7.1.25 - 7.1.28, 7.2.0 - 7.2.33, 7.3.0 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.0 - 8.1.33, 8.2.0 - 8.2.29, 8.3.0 - 8.3.26, 8.4.1 - 8.4.13
array(2) { [0]=> int(12345) [1]=> int(45673) }

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