Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Calculation/MathTrig.php
public static function COMBIN($numObjs, $numInSet)
    {
        $numObjs = Functions::flattenSingleValue($numObjs);
        $numInSet = Functions::flattenSingleValue($numInSet);

        if ((is_numeric($numObjs)) && (is_numeric($numInSet))) {
            if ($numObjs < $numInSet) {
                return Functions::NAN();
            } elseif ($numInSet < 0) {
                return Functions::NAN();
            }

            return round(self::FACT($numObjs) / self::FACT($numObjs - $numInSet)) / self::FACT($numInSet);
        }

        return Functions::VALUE();
    }
public static function COMBIN($numObjs, $numInSet)
    {
        $numObjs = Functions::flattenSingleValue($numObjs);
        $numInSet = Functions::flattenSingleValue($numInSet);

        if ((is_numeric($numObjs)) && (is_numeric($numInSet))) {
            if ($numObjs < $numInSet) {
                return Functions::NAN();
            } elseif ($numInSet < 0) {
                return Functions::NAN();
            }

            return round(self::FACT($numObjs) / self::FACT($numObjs - $numInSet)) / self::FACT($numInSet);
        }

        return Functions::VALUE();
    }
COMBIN.

Returns the number of combinations for a given number of items. Use COMBIN to
determine the total possible number of groups for a given number of items.

Excel Function:
COMBIN(numObjs,numInSet)

@category Mathematical and Trigonometric Functions

@param int $numObjs Number of different objects
@param int $numInSet Number of objects in each combination

@return int Number of combinations