concatenate pdf files with ubunbtu

$ pdfunite ES_0818_1.pdf ES_0818_2.pdf  ES_0818_3.pdf  ex_082018.pdf

In order to remove an (unknown) password from a protected pdf use this command:
$ gs -q -dNOPAUSE -dBATCH -sDEVICE=pdfwrite -sOutputFile=unencrypted.pdf -c .setpdfwrite -f encrypted.pdf

factorial with RecursiveTask

	import java.util.concurrent.ForkJoinPool;
	import java.util.concurrent.ForkJoinTask;
	import java.util.concurrent.RecursiveTask;
	/**
	* Created by enrico on 12/21/16.
	*/
	public class Factorial {
	private static class FactorialTask extends RecursiveTask<Long>{
	long n;
	private FactorialTask(long n){
	this.n = n;
	}
	@Override
	protected Long compute() {
	if(n<=1) return 1L;
	FactorialTask ft = new FactorialTask(n-1);
	ft.fork();
	return n * ft.join();
	}
	}
	public long factorial(long n){
	ForkJoinTask<Long> fjt = new FactorialTask(n);
	ForkJoinPool pool = new ForkJoinPool();
	return pool.invoke(fjt);
	}
	public static void main(String[] args) {
	long result = new Factorial().factorial(5);
	System.out.println(result);
	}
	}

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