5
This number is a prime.
Just showing those entries submitted by 'Capelle': (Click here to show all)
The smallest odd prime equal to the sum of two squares and
to the arithmetic mean of two squares. [Capelle]
There are 5 families of butterflies. [Capelle]
The number of known strobogrammatic squares. The number of
distinct digits to write them. [Capelle]
The largest Pell number (coincidentally prime) of the
form x2 + 1. Note that 5 =
22 + 1, where 1 and 2 are the
two other Pell numbers of this form. [Capelle]
The only prime of the form 4n + n4, where n is a positive
integer. [Capelle]
Every positive integer can be written as the sum of 5
pentagonal numbers. Note that 5 is the only prime
pentagonal number. [Capelle]
The only known prime p such that sigma(p) divides
sigma(sigma(p)). [Capelle]
The only prime p such that phi(p) = tau(p) + 2, phi(p) = tau(p) * 2, and phi(p) = tau(p)2. [Capelle]
The largest known prime p such that fib(p) divides p!, but
the only prime equal to fib(p). [Capelle]
There are 5 natural numbers n such that n is equal to the
number of 5's in the decimal digits of all natural numbers
smaller or equal to n. [Capelle]
Pollock's
conjecture (1850) states that every number can be written as the sum of at most five tetrahedral
numbers. No connection with the famous painting No.
5, 1948, by Jackson Pollock. [Capelle]
The largest known prime number p such that binomial(2p,p) is cubefree. [Capelle]