20815 has 8 divisors (see below), whose sum is σ = 26208. Its totient is φ = 15840.

The previous prime is 20809. The next prime is 20849. The reversal of 20815 is 51802.

20815 = T₄ + T₅ + ... + T₄₉.

20815 = 30² + 31² + ... + 44².

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 20815 - 2³ = 20807 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 13.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 25 + ... + 205.

It is an arithmetic number, because the mean of its divisors is an integer number (3276).

2²⁰⁸¹⁵ is an apocalyptic number.

20815 is a deficient number, since it is larger than the sum of its proper divisors (5393).

20815 is a wasteful number, since it uses less digits than its factorization.

20815 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 209.

The product of its (nonzero) digits is 80, while the sum is 16.

The square root of 20815 is about 144.2740447898. The cubic root of 20815 is about 27.5079866610.

The spelling of 20815 in words is "twenty thousand, eight hundred fifteen".