20561231 has 4 divisors (see below), whose sum is σ = 20998752. Its totient is φ = 20123712.

The previous prime is 20561221. The next prime is 20561237. The reversal of 20561231 is 13216502.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 20561231 - 2¹⁰ = 20560207 is a prime.

It is a super-2 number, since 2×20561231² = 845528440470722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20561237) 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, 218690 + ... + 218783.

It is an arithmetic number, because the mean of its divisors is an integer number (5249688).

Almost surely, 2^20561231 is an apocalyptic number.

20561231 is a deficient number, since it is larger than the sum of its proper divisors (437521).

20561231 is an equidigital number, since it uses as much as digits as its factorization.

20561231 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 437520.

The product of its (nonzero) digits is 360, while the sum is 20.

The square root of 20561231 is about 4534.4493601759. The cubic root of 20561231 is about 273.9574009822.

Adding to 20561231 its reverse (13216502), we get a palindrome (33777733).

The spelling of 20561231 in words is "twenty million, five hundred sixty-one thousand, two hundred thirty-one".