Newman–Shanks–Williams prime

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In mathematics, a Newman–Shanks–Williams prime (NSW prime) is a prime number p which can be written in the form

$S_{{2m+1}}={\frac {\left(1+{\sqrt {2}}\right)^{{2m+1}}+\left(1-{\sqrt {2}}\right)^{{2m+1}}}{2}}.$

NSW primes were first described by Morris Newman, Daniel Shanks and Hugh C. Williams in 1981 during the study of finite simple groups with square order.

The first few NSW primes are 7, 41, 239, 9369319, 63018038201, … (sequence A088165 in OEIS), corresponding to the indices 3, 5, 7, 19, 29, … (sequence A005850 in OEIS).

The sequence S alluded to in the formula can be described by the following recurrence relation:

$S_{0}=1\,$

$S_{1}=1\,$

$S_{n}=2S_{{n-1}}+S_{{n-2}}\qquad {\text{for all }}n\geq 2.$

The first few terms of the sequence are 1, 1, 3, 7, 17, 41, 99, … (sequence A001333 in OEIS). Each term in this sequence is half the corresponding term in the sequence of companion Pell numbers. These numbers also appear in the continued fraction convergents to √2.

External links

The Prime Glossary: NSW number

v t e Prime number classes

By formula	Fermat (2^2ⁿ + 1) Mersenne (2^p − 1) Double Mersenne (2^{2^p−1} − 1) Wagstaff (2^p + 1)/3 Proth (k·2ⁿ + 1) Factorial (n! ± 1) Primorial (p_n# ± 1) Euclid (p_n# + 1) Pythagorean (4n + 1) Pierpont (2^u·3^v + 1) Solinas (2^a ± 2^b ± 1) Cullen (n·2ⁿ + 1) Woodall (n·2ⁿ − 1) Cuban (x³ − y³)/(x − y) Carol (2ⁿ − 1)² − 2 Kynea (2ⁿ + 1)² − 2 Leyland (x^y + y^x) Thabit (3·2ⁿ − 1) Mills (floor(A^3ⁿ))

By integer sequence	Fibonacci Lucas Motzkin Bell Partitions Pell Perrin Newman–Shanks–Williams

By property	Lucky Wall–Sun–Sun Wilson Wieferich Wieferich pair Fortunate Ramanujan Pillai Regular Strong Stern Supersingular (elliptic curve) Supersingular (moonshine theory) Wolstenholme Good Super Higgs Highly cototient Illegal

Base-dependent	Happy Dihedral Palindromic Emirp Repunit (10ⁿ − 1)/9 Permutable Circular Truncatable Strobogrammatic Minimal Full reptend Unique Primeval Self Smarandache–Wellin

Patterns	Twin (p, p + 2) Bi-twin chain (p − 1, p + 1, 2p − 1, 2p + 1, …) Triplet (p, p + 2 or p + 4, p + 6) Quadruplet (p, p + 2, p + 6, p + 8) Tuple Cousin (p, p + 4) Sexy (p, p + 6) Chen Sophie Germain (p, 2p + 1) Cunningham chain (p, 2p ± 1, …) Safe (p, (p − 1)/2) Arithmetic progression (p + a·n, n = 0, 1, …) Balanced (consecutive p − n, p, p + n)

By size	Titanic (1,000+ digits) Gigantic (10,000+) Mega (1,000,000+) Largest known

Complex numbers	Eisenstein prime Gaussian prime

Composite numbers	Pseudoprime Almost prime Semiprime Interprime

Related topics	Probable prime Industrial-grade prime Formula for primes Prime gap

List of prime numbers

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Newman–Shanks–Williams prime

Further reading

External links