r"""
Python module for OEIS sequence number A052008.

'n with digits sorted ascending' + 'n with digits sorted descending'.

Examples of use.
-----------------------------------------------------------------------
>>> from a052008 import *
>>> print a052008_list(16)
[2, 4, 6, 8, 10, 12, 14, 16, 18, 11, 22, 33, 44, 55, 66, 77]
>>> print a052008_offset
0
>>> for x in a052008_list_pairs(6):
...     print x
...
(0, 2)
(1, 4)
(2, 6)
(3, 8)
(4, 10)
(5, 12)
>>> print a052008(5)
12
-----------------------------------------------------------------------
"""

from itertools import islice, izip, count

__all__ = ('a052008_offset', 'a052008_list', 'a052008_list_pairs', 'a052008', 'a052008_gen')
__author__ = 'Nick Hobson <nickh@qbyte.org>'

a052008_offset = offset = 0

def a052008_gen():
    """Generator function for OEIS sequence A052008."""
    for n in count(1):
        z = []
        while n > 0:
            n, d = divmod(n, 10)
            z.append(d)
        z.sort()
        x = reduce(lambda s, t: 10*s + t, z) + reduce(lambda s, t: 10*s + t, reversed(z))
        yield x

def a052008_list(n):
    """Returns a list of the first n >= 0 terms."""
    if n < 0: raise ValueError, 'Input must be a non-negative integer'
    return list(islice(a052008_gen(), n))

def a052008_list_pairs(n):
    """Returns a list of tuples (n, a(n)) of the first n >= 0 terms."""
    if n < 0: raise ValueError, 'Input must be a non-negative integer'
    return list(izip(xrange(offset, n+offset), a052008_gen()))

def a052008(n):
    """Returns the term with index n >= 0; offset 0."""
    if n < offset: raise ValueError, 'Input must be an integer >= offset = ' + str(offset)
    return list(islice(a052008_gen(), n-offset, n-offset+1)).pop()