Pell Number | Calculate nth pell number ; Driver function
def pell ( n ) : NEW_LINE INDENT if ( n <= 2 ) : NEW_LINE INDENT return n NEW_LINE DEDENT return ( 2 * pell ( n - 1 ) + pell ( n - 2 ) ) NEW_LINE DEDENT n = 4 ; NEW_LINE print ( pell ( n ) ) NEW_LINE