<?php
$a = array(1, 2, 4, 6, 8, 9, 10, 15, 16, 17, 20, 21, 23, 24, 26, 27, 28, 29, 31, 39);
 
$maiorDistancia = 0;
$sequencias = [];
$ultimaSeq = 0;
 
for ($i = 0; $i < count($a)-1; ++$i){
    $dist = abs($a[$i]-$a[$i+1]);
 
    if ($dist > $maiorDistancia) $maiorDistancia = $dist;
 
    if (($a[$i+1]-$a[$i]) == 1){
        if (isset($sequencias[$ultimaSeq])){
            $sequencias[$ultimaSeq][] = $a[$i+1];
        }
        else {
            $sequencias[$ultimaSeq][0] = $a[$i];
            $sequencias[$ultimaSeq][1] = $a[$i+1];
        }
    }
    else {
        $ultimaSeq++;
    }
}
 
echo ("Maior distancia: $maiorDistancia \n Sequencias: ");
 
print_r($sequencias);

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