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# References

References are bibliographic citations for materials, such as books and journals, which might not be primarily available on the Web. OEIS sequence entries have a field for references (%D lines in the internal format).

Unlike certain scientific or mathematical journals, the OEIS does not have a rigidly enforced citation style. The important thing is for the following information to be present:

• Name(s) of the author(s)
• Title of the book or article
• Year of publication
• Information needed to find the relevant issue or section, such as volume number
• Information needed to find the relevant paragraph(s), such as page number(s)

So, for example, "some page in that famous book by Don Knuth" would be unacceptable as a reference. On the other hand, "page 189 in Volume 2 of The Art of Computer Programming, 1969" might just barely pass muster. Although it might be a good idea to try to follow APA or MLA style, there is no need to get excessively fussy in following every rule that could possibly apply.

The following example comes from A218459, ${\displaystyle a(n)}$ is the smallest positive integer ${\displaystyle d}$ such that ${\displaystyle p_{n}=x^{2}+dy^{2}}$ has a solution ${\displaystyle (x,y)}$ in integers, where ${\displaystyle p_{n}}$ is the ${\displaystyle n}$th prime:

 References Ethan D. Bolker, Elementary Number Theory: An Algebraic Approach. Mineola, New York: Dover Publications (1969, reprinted 2007): p. 68, Theorem 24.5; p. 74, Theorem 25.4. D. Cox, "Primes of Form x^2 + n y^2", Wiley, 1989, Section 9, "Ring class fields and p = x^2 + n y^2."

In the case of something that is primarily available as a Web page, it is preferable to use the Links field. However, as books are becoming increasingly available online, the distinction between references and links is blurred and there has been discussion on Seqfan as to whether the OEIS should keep up this distinction.

In any case, if there is a digital object identifier (DOI) available, which is the case for most published books and articles, it should at least be given along with the reference (as, e.g., "doi:10.1007/978-1-4899-3585-4"), unless the contributor wants to move the reference to the LINKS section and convert the DOI to a link be appending it to the prefix "http://dx.doi.org/".

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