Everything about Woodall Prime totally explained
In
mathematics, a
Woodall number is a
natural number of the form
n · 2
n − 1 (written
Wn). Woodall numbers were first studied by
Allan J. C. Cunningham and
H. J. Woodall in
1917, inspired by
James Cullen's earlier study of the similarly-defined
Cullen numbers. The first few Woodall numbers are
1,
7,
23,
63, 159, 383, 895, ... .Woodall numbers curiously arise in
Goodstein's theorem.
Woodall numbers that are also
prime numbers are called
Woodall primes; the first few exponents
n for which the corresponding Woodall numbers
Wn are prime are 2, 3, 6, 30, 75, 81, 115, 123, 249, 362, 384, ... ; the Woodall primes themselves begin with 7, 23, 383, 32212254719, ... .
Like
Cullen numbers, Woodall numbers have many divisibility properties. For example, if
p is a prime number, then
p divides
» W(p + 1) / 2 if the
Jacobi symbol is −1.
It is conjectured that
almost all Woodall numbers are
composite; a
proof has been submitted by H. Suyama, but it hasn't been verified yet. Nonetheless, it's also conjectured that there are infinitely many Woodall primes.
As of December 2007, the largest known Woodall prime is 3752948 · 2
3752948 − 1. It has 1129757 digits and was found by Matthew J Thompson in 2007 in the
distributed computing project
PrimeGrid.
A
generalized Woodall number is defined to be a number of the form
n ·
bn − 1, where
n + 2 >
b; if a prime can be written in this form, it's then called a
generalized Woodall prime.
Further Information
Get more info on 'Woodall Prime'.
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