simple Collatz Conjecture in node

collatz.js

#! /usr/local/bin/node

var sys = require('sys'),
    iter = [],
    start = (process.argv.length > 2) ? parseInt(process.argv[2], 10) : null,
    stdin;

function askForNumber() {
    sys.print('enter a number: ');
    if (stdin) {
        stdin.resume();
    } else {
        stdin = process.openStdin();
        stdin.setEncoding('utf8');
        stdin.on('data', function(data) {
            stdin.pause();
            start = parseInt(data, 10);
            if (isNaN(start)) {
                sys.puts(data.trim() + ' is not a number');
                askForNumber();
            } else {
                stdin.destroy();
                collatz(start);
            }
        });
    }
}

function collatz(n) {
    iter[iter.length] = n;
    if (n !== 1) {
        n%2 ? collatz(3*n + 1) : collatz(n/2);
    } else {
        sys.puts('\n' + iter.join(' -> ') + '\n\n' + start + ' converged to 1 in ' + (iter.length - 1) + ' iterations');
    }
}

if (!start || isNaN(start)) {
    askForNumber();
} else {
    collatz(start);
}