OEIS Tools
==========

This repository contains scripts to download, process, and analyze data from the
Online Encyclopedia of Integer Sequences (OEIS), as hosted on http://www.oeis.org.

Overview
--------

Our tools handle OEIS data from three sources:

1. remote: the OEIS database residing on the oeis.org server. The remote database can be accessed via HTTP or HTTPS requests.
2. local sqlite3: a replica of the remote database as a local SQLite3 database file.
3. local pickle: the OEIS database a a local pickle-format file, used for local analysis. The "pickle" format is Python-specific.

The local sqlite3 database is obtained from the remote database by an automatic web-crawler called 'fetch_oeis_database.py'.
It contains the sequence metadata in the internal format as it is used on the remote side, as well as so called 'b-file'
data that contain sequence data *a(n)* up to high values of *n*.

The local pickle format database is obtained from the local_sqlite3 database by parsing the data and turning it into OeisEntry
instances. The pickled list of all OeisEntry instances can be read in its entirety within a few seconds.

Apart from these sources that describe the OEIS data, we also use the "catalog", which is a Python module that contains
implementations of sequence generating functions.

Dependencies
------------

- All code is written in Python 3.
- Some code depends on the 'numpy' library:
  - show_database_time.py
  - solve_linear_sequence.py
- Some code depends on the 'matplotlib' library:
  - show_database_time.py

Description of files
--------------------

Non-Python files:

filename                          |  description
----------------------------------|------------------------------------------------------------------------------------
README.md                         |  Text file (markdown format) description of the project.
catalog_files/*.json              |  Catalog files, describing parametrized sequence generating functions.

Python scripts files:

filename                          |  description
----------------------------------|------------------------------------------------------------------------------------
fetch_oeis_database.py            |  Fetch and refresh data from the remote OEIS database to a local sqlite3 database.
show_database_time.py             |  Visualize time stamps in a given local sqlite3 OEIS database.
parse_oeis_database.py            |  Parse a local sqlite3 database and produce a local pickle database.
find_sequences.py                 |  Probe a local pickle database for a given sequence (work in progress).
pickle_to_json.py                 |  Read a local pickle database and write a JSON version.
solve_linear_sequence.py          |  Find linear sequences in a local 'pickle' database.
check_database.py                 |  Perform a number of checks on the data in a local pickle database.
verify_oeis_catalog.py            |  Verify the catalog.

Python modules:

filename                          |  description
----------------------------------|------------------------------------------------------------------------------------
fraction_based_linear_algebra.py  |  Perform matrix inversion without loss of precision using the Fraction type.
charmap.py                        |  Defines lists of acceptable characters for the OEIS directives.
OeisEntry.py                      |  Defines a simple class that contains (most of) the data of a single OEIS sequence.
timer.py                          |  Simplifies timing lengthy operations using a context manager.
fetch_remote_oeis_entry.py        |  Fetches a single sequence's data from the OEIS website (www.oeis.org).
catalog.py                        |  Access the local catalog.

How it all fits together
------------------------

<img alt="Overview of OEIS tools" src="docs/oeis-tools.png" width="75%">