r"""
Python module for OEIS sequence number A003608.

Add 4, then reverse digits.

Examples of use.
-----------------------------------------------------------------------
>>> from a003608 import *
>>> print a003608_list(16)
[0, 4, 8, 21, 52, 65, 96, 1, 5, 9, 31, 53, 75, 97, 101, 501]
>>> print a003608_offset
0
>>> for x in a003608_list_pairs(6):
...     print x
...
(0, 0)
(1, 4)
(2, 8)
(3, 21)
(4, 52)
(5, 65)
>>> print a003608(5)
65
-----------------------------------------------------------------------
"""

from itertools import islice, izip

__all__ = ('a003608_offset', 'a003608_list', 'a003608_list_pairs', 'a003608', 'a003608_gen')
__author__ = 'Nick Hobson <nickh@qbyte.org>'

a003608_offset = offset = 0

def a003608_gen(k):
    """Generator function for OEIS sequence A003608."""
    x = 0
    while True:
        yield x
        x = int(str(x + k)[::-1])

def a003608_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(a003608_gen(4), n))

def a003608_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), a003608_gen(4)))

def a003608(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(a003608_gen(4), n-offset, n-offset+1)).pop()