20621 has 4 divisors (see below), whose sum is σ = 21852. Its totient is φ = 19392.

The previous prime is 20611. The next prime is 20627. The reversal of 20621 is 12602.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12602 = 2 ⋅6301.

It can be written as a sum of positive squares in 2 ways, for example, as 7396 + 13225 = 86^2 + 115^2 .

It is a cyclic number.

It is not a de Polignac number, because 20621 - 2¹⁰ = 19597 is a prime.

It is a Duffinian number.

It is a Curzon number.

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 20621.

It is not an unprimeable number, because it can be changed into a prime (20627) 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, 590 + ... + 623.

It is an arithmetic number, because the mean of its divisors is an integer number (5463).

2²⁰⁶²¹ is an apocalyptic number.

It is an amenable number.

20621 is a deficient number, since it is larger than the sum of its proper divisors (1231).

20621 is a wasteful number, since it uses less digits than its factorization.

20621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1230.

The product of its (nonzero) digits is 24, while the sum is 11.

The square root of 20621 is about 143.6001392757. The cubic root of 20621 is about 27.4222597808.

The spelling of 20621 in words is "twenty thousand, six hundred twenty-one".