Return bordering French area from one area number

func_bordering_areas.php

<?php
/**
 * Return bordering french area from one area number
 * Thanks to https://gist.github.com/sunny/13803 for inspiration
 * 
 * @param $areaNumber
 * @return mixed
 */
function bordering_areas($areaNumber) {
    $borderingAreas = [
        '01' => ['38', '39', '69', '71', '73', '74'],
        '02' => ['08', '51', '59', '60', '77', '80'],
        '03' => ['18', '23', '42', '58', '63', '71'],
        '04' => ['05', '06', '13', '26', '83', '84'],
        '05' => ['04', '26', '38', '73'],
        '06' => ['04', '83'],
        '07' => ['26', '30', '38', '42', '43', '48', '84'],
        '08' => ['02', '51', '55'],
        '09' => ['11', '31', '66'],
        '10' => ['21', '51', '52', '77', '89'],
        '11' => ['09', '31', '34', '66', '81'],
        '12' => ['15', '30', '34', '46', '48', '81', '82'],
        '13' => ['04', '30', '83', '84'],
        '14' => ['27', '50', '61', '76'],
        '15' => ['12', '19', '43', '46', '48', '63'],
        '16' => ['17', '24', '79', '86', '87'],
        '17' => ['16', '24', '33', '79', '85'],
        '18' => ['03', '23', '36', '41', '45', '58'],
        '19' => ['15', '23', '24', '46', '63', '87'],
        '2A' => ['2B'],
        '2B' => ['2A'],
        '21' => ['10', '39', '52', '58', '70', '71', '89'],
        '22' => ['29', '35', '56'],
        '23' => ['03', '18', '19', '36', '63', '87'],
        '24' => ['16', '17', '19', '33', '46', '47', '87'],
        '25' => ['39', '70', '90'],
        '26' => ['04', '05', '07', '38', '84'],
        '27' => ['14', '28', '60', '61', '76', '78', '95'],
        '28' => ['27', '41', '45', '61', '72', '78', '91'],
        '29' => ['22', '56'],
        '30' => ['07', '12', '13', '34', '48', '84'],
        '31' => ['09', '11', '32', '65', '81', '82'],
        '32' => ['31', '40', '47', '64', '65', '82'],
        '33' => ['17', '24', '40', '47'],
        '34' => ['11', '12', '30', '81'],
        '35' => ['22', '44', '49', '50', '53', '56'],
        '36' => ['18', '23', '37', '41', '86', '87'],
        '37' => ['36', '41', '49', '72', '86'],
        '38' => ['01', '05', '07', '26', '42', '69', '73'],
        '39' => ['01', '21', '25', '70', '71'],
        '40' => ['32', '33', '47', '64'],
        '41' => ['18', '28', '36', '37', '45', '72'],
        '42' => ['03', '07', '38', '43', '63', '69', '71'],
        '43' => ['07', '15', '42', '48', '63'],
        '44' => ['35', '49', '56', '85'],
        '45' => ['18', '28', '41', '58', '77', '89', '91'],
        '46' => ['12', '15', '19', '24', '47', '82'],
        '47' => ['24', '32', '33', '40', '46', '82'],
        '48' => ['07', '12', '15', '30', '43'],
        '49' => ['35', '37', '44', '53', '72', '79', '85', '86'],
        '50' => ['14', '35', '53', '61'],
        '51' => ['02', '08', '10', '52', '55', '77'],
        '52' => ['10', '21', '51', '55', '70', '88'],
        '53' => ['35', '49', '50', '61', '72'],
        '54' => ['55', '57', '67', '88'],
        '55' => ['08', '51', '52', '54', '88'],
        '56' => ['22', '29', '35', '44'],
        '57' => ['54', '67'],
        '58' => ['03', '18', '21', '45', '71', '89'],
        '59' => ['02', '62', '80'],
        '60' => ['02', '27', '76', '77', '80', '95'],
        '61' => ['14', '27', '28', '50', '53', '72'],
        '62' => ['59', '80'],
        '63' => ['03', '15', '19', '23', '42', '43'],
        '64' => ['32', '40', '65'],
        '65' => ['31', '32', '64'],
        '66' => ['09', '11'],
        '67' => ['54', '57', '68', '88'],
        '68' => ['67', '88', '90'],
        '69' => ['01', '38', '42', '71'],
        '70' => ['21', '25', '39', '52', '88', '90'],
        '71' => ['01', '03', '21', '39', '42', '58', '69'],
        '72' => ['28', '37', '41', '49', '53', '61'],
        '73' => ['01', '05', '38', '74'],
        '74' => ['01', '73'],
        '75' => ['92', '93', '94'],
        '76' => ['14', '27', '60', '80'],
        '77' => ['02', '10', '45', '51', '60', '89', '91', '93', '94', '95'],
        '78' => ['27', '28', '91', '92', '95'],
        '79' => ['16', '17', '49', '85', '86'],
        '80' => ['02', '59', '60', '62', '76'],
        '81' => ['11', '12', '31', '34', '82'],
        '82' => ['12', '31', '32', '46', '47', '81'],
        '83' => ['04', '06', '13', '84'],
        '84' => ['04', '07', '13', '26', '30', '83'],
        '85' => ['17', '44', '49', '79'],
        '86' => ['16', '36', '37', '49', '79', '87'],
        '87' => ['16', '19', '23', '24', '36', '86'],
        '88' => ['52', '54', '55', '67', '68', '70', '90'],
        '89' => ['10', '21', '45', '58', '77'],
        '90' => ['25', '68', '70', '88'],
        '91' => ['28', '45', '77', '78', '92', '94'],
        '92' => ['75', '78', '91', '93', '94', '95'],
        '93' => ['75', '77', '92', '94', '95'],
        '94' => ['75', '77', '91', '92', '93'],
        '95' => ['27', '60', '77', '78', '92', '93']
    ];
    return $borderingAreas[$areaNumber];
}