20651 has 4 divisors (see below), whose sum is σ = 20952. Its totient is φ = 20352.

The previous prime is 20641. The next prime is 20663. The reversal of 20651 is 15602.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20651 is a prime.

It is an Ulam number.

It is a Duffinian number.

It is a nialpdrome in base 14.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 20651.

It is not an unprimeable number, because it can be changed into a prime (20611) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 11 + ... + 203.

It is an arithmetic number, because the mean of its divisors is an integer number (5238).

2²⁰⁶⁵¹ is an apocalyptic number.

20651 is a deficient number, since it is larger than the sum of its proper divisors (301).

20651 is a wasteful number, since it uses less digits than its factorization.

20651 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 300.

The product of its (nonzero) digits is 60, while the sum is 14.

The square root of 20651 is about 143.7045580349. The cubic root of 20651 is about 27.4355515573.

The spelling of 20651 in words is "twenty thousand, six hundred fifty-one".