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9 results for “prime”

Formulae (9)

BMI\ prime = \frac{BMI}{25}

Your BMI relative to the upper healthy limit.

a^{p-1} \equiv 1 \pmod{p}

Holds when p is prime and gcd(a,p)=1.

\phi(n) = n\prod_{p|n}\left(1 - \frac{1}{p}\right)

Counts integers up to n coprime to n.

\pi(x) \sim \frac{x}{\ln x}

Approximates the number of primes below x.

d(n) = \prod (a_i + 1)

Count of divisors from prime factorization exponents.

\sigma(n) = \prod \frac{p_i^{a_i+1}-1}{p_i - 1}

Sum of all divisors from prime factorization.

M_p = 2^p - 1

Numbers one less than a power of two.

F_n = 2^{2^n} + 1

Numbers of a special exponential form.

(p-1)! \equiv -1 \pmod{p}

A primality criterion for p.