r"""
Python module for OEIS sequence number A019463.

Add 1, multiply by 1, add 2, multiply by 2, and so on.

Examples of use.
-----------------------------------------------------------------------
>>> from a019463 import *
>>> print a019463_list(14)
[1, 2, 2, 4, 8, 11, 33, 37, 148, 153, 765, 771, 4626, 4633]
>>> print a019463_offset
0
>>> for x in a019463_list_pairs(6):
...     print x
...
(0, 1)
(1, 2)
(2, 2)
(3, 4)
(4, 8)
(5, 11)
>>> print a019463(5)
11
-----------------------------------------------------------------------
"""

from itertools import islice, izip, count
from a019460 import a019460_gen

__all__ = ('a019463_offset', 'a019463_list', 'a019463_list_pairs', 'a019463', 'a019460_gen')
__author__ = 'Nick Hobson <nickh@qbyte.org>'

a019463_offset = offset = 0

def a019463_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(a019460_gen(1), n))

def a019463_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), a019460_gen(1)))

def a019463(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(a019460_gen(1), n-offset, n-offset+1)).pop()