20649 has 4 divisors (see below), whose sum is σ = 27536. Its totient is φ = 13764.

The previous prime is 20641. The next prime is 20663. The reversal of 20649 is 94602.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 20649 - 2³ = 20641 is a prime.

It is a D-number.

It is a Duffinian number.

It is a Curzon number.

20649 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (20641) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3439 + ... + 3444.

It is an arithmetic number, because the mean of its divisors is an integer number (6884).

2²⁰⁶⁴⁹ is an apocalyptic number.

It is an amenable number.

20649 is a deficient number, since it is larger than the sum of its proper divisors (6887).

20649 is an equidigital number, since it uses as much as digits as its factorization.

20649 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6886.

The product of its (nonzero) digits is 432, while the sum is 21.

The square root of 20649 is about 143.6975991449. The cubic root of 20649 is about 27.4346658395.

The spelling of 20649 in words is "twenty thousand, six hundred forty-nine".