20531 has 6 divisors (see below), whose sum is σ = 23940. Its totient is φ = 17556.

The previous prime is 20521. The next prime is 20533. The reversal of 20531 is 13502.

It is not a de Polignac number, because 20531 - 2¹⁰ = 19507 is a prime.

It is a super-2 number, since 2×20531² = 843043922, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (20533) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 161 + ... + 258.

It is an arithmetic number, because the mean of its divisors is an integer number (3990).

2²⁰⁵³¹ is an apocalyptic number.

20531 is a deficient number, since it is larger than the sum of its proper divisors (3409).

20531 is an equidigital number, since it uses as much as digits as its factorization.

20531 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 433 (or 426 counting only the distinct ones).

The product of its (nonzero) digits is 30, while the sum is 11.

The square root of 20531 is about 143.2864264332. The cubic root of 20531 is about 27.3823069393.

The spelling of 20531 in words is "twenty thousand, five hundred thirty-one".