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Getting Started with OEIS.R

Enrique Pérez Herrero

2026-07-19

Source: vignettes/OEIS.R-Getting-Started.Rmd
OEIS.R-Getting-Started.Rmd

Note: oeis.org was not reachable while this copy of the vignette was built, so the code chunks below are shown but were not run and display no output.

Introduction

The On-Line Encyclopedia of Integer Sequences (OEIS) is a database of over 390,000 integer sequences, each documented with a description, formulae, references, links, and example code in several languages. OEIS.R fetches a sequence’s entry from oeis.org and parses it into structured R objects, so it can be explored, cited, and plotted without leaving R.

Because every function in this vignette talks to oeis.org directly (there are no bundled fixtures), building it requires an internet connection, and the output you see reflects the live state of OEIS at build time. Please respect OEIS’s terms of use and avoid hammering the server with tight loops over many sequences.

Installation 

# install.packages("devtools")
devtools::install_github("EnriquePH/OEIS.R")

Loading the package

OEIS urls 

OEIS_web_url()
OEIS_web_url(license = TRUE)

OEIS_search_url() builds a URL for a free-text search of the encyclopedia:

OEIS_search_url("Dedekind psi function")

Number of sequences in the encyclopedia

Fetching a sequence

The OEIS_sequence S3 class

OEIS_sequence() takes an ID (a string of the form "A" followed by 6 digits) and downloads and parses the sequence’s full entry:

id <- "A001615"
A001615 <- OEIS_sequence(id)
class(A001615)
names(A001615)

An invalid ID is rejected up front, before any network request is made:

OEIS_check("hello")

Basic sequence information 

A001615$ID
A001615$description
A001615$formerly   # old M-/N-number from Sloane's printed catalogs
A001615$offset
A001615$keywords
A001615$status
A001615$url

Author and date 

A001615$author

Not every entry has a parseable trailing date on its author line — when it doesn’t, $date is NULL rather than a Date:

A001615$date

A138240 <- OEIS_sequence("A138240")
A138240$date

Terms

$terms holds the (typically 50-80) leading terms shown on the sequence’s page:

head(A001615$terms, 15)

For longer runs, use the sequence’s b-file, which OEIS provides separately and which this package downloads via OEIS_bfile():

A001615$bfile$min_n
A001615$bfile$max_n
head(A001615$bfile$data)
length(A001615$comments)
A001615$comments[1]

length(A001615$formula)
A001615$formula[1:3]
library(knitr)
kable(data.frame(link = A001615$links[1:5]))

Cross references

Besides the sequences explicitly referenced in the entry’s CROSSREFS section ($cf), OEIS also shows the neighboring sequences in lexicographic order ($seqs_in_context) and by A-number ($seqs_adjacent):

A001615$crossrefs$cf
A001615$crossrefs$seqs_in_context
A001615$crossrefs$seqs_adjacent

Plotting

Base R 

plot(A001615)

ggplot2

OEIS_ggplot() plots the full b-file (not just the leading terms shown above) and returns a normal ggplot object you can extend:

library(ggplot2)

OEIS_ggplot(A001615) +
  geom_line() +
  geom_point(size = 0.5, color = "green") +
  labs(title = paste("OEIS", id, "-", A001615$description))

Citing a sequence

OEIS_bibtex() builds a citable bibentry for a sequence, following the citation format suggested by OEIS itself:

bref <- OEIS_bibtex(A001615)
print(bref, style = "Bibtex")
bref$note

Working from just an ID

Every accessor used above (OEIS_description(), OEIS_formula(), …) also works directly on a character ID, without building the full OEIS_sequence object first — useful when you only need one or two fields and want to avoid the extra requests OEIS_sequence() makes (crossrefs and b-file, in particular, each cost a separate request):

Internally, a character ID is validated into an OEIS_ID object and then, for most fields, converted to the sequence’s parsed internal format (OEIS’s compact %-tagged export format). You can inspect that intermediate object directly:

internal_format <- OEIS_internal_format(id)
class(internal_format)
head(internal_format)

Session info