<?php
/**
 * Segue abaixo a implementacao das funcoes (escitra em apenas uma linha) para
 * calcular a sequencia de Fibonacci, Tribonacci e Tetranacci.
 *
 * Below follows the implementation of the functions (written in a single line) to
 * calculate the Fibonacci, Tribonacci and Tetranacci sequences.
 *
 * @category    Math
 * @author      Arthur Furlan <arthur.furlan@gmail.com>
 * @link        http://arthurfurlan.org/phpday/fibonacci.php.txt
 * @license     http://www.gnu.org/licenses/gpl.txt GNU Public License
 * @see         http://pt.wikipedia.org/wiki/N%C3%BAmero_de_Fibonacci
 */

function fibonacci($n) {
    return $n < 0 ? false : $n < 2 ? $n : fibonacci($n-1) + fibonacci($n-2);
}

function tribonacci($n) {
    return $n < 0 ? false : $n < 3 ? fibonacci($n) : tribonacci($n-1) + tribonacci($n-2) + tribonacci($n-3);
}

function tetranacci($n) {
    return $n < 0 ? false : $n < 4 ? fibonacci($n) : tetranacci($n-1) + tetranacci($n-2) + tetranacci($n-3) + tetranacci($n-4);
}
?>