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<?php function isSequential(array $sequence, $diff = 1) { return $sequence[count($sequence) - 1] === $sequence[0] + ($diff * (count($sequence) - 1)); } $a = [5,7,8,9,10]; $b = [2,3,4,5,6,7,8,9,10]; $c = [10]; $d = [2,4,6,8,10,12]; var_dump(isSequential($a)); var_dump(isSequential($b)); var_dump(isSequential($c)); var_dump(isSequential($d, 2));