20631581 has 4 divisors (see below), whose sum is σ = 20641500. Its totient is φ = 20621664.

The previous prime is 20631577. The next prime is 20631599. The reversal of 20631581 is 18513602.

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 can be written as a sum of positive squares in 2 ways, for example, as 7425625 + 13205956 = 2725^2 + 3634^2 .

It is a cyclic number.

It is not a de Polignac number, because 20631581 - 2² = 20631577 is a prime.

It is a super-2 number, since 2×20631581² = 851324269119122, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 20631581.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20631571) 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, 506 + ... + 6443.

It is an arithmetic number, because the mean of its divisors is an integer number (5160375).

Almost surely, 2^20631581 is an apocalyptic number.

It is an amenable number.

20631581 is a deficient number, since it is larger than the sum of its proper divisors (9919).

20631581 is an equidigital number, since it uses as much as digits as its factorization.

20631581 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9918.

The product of its (nonzero) digits is 1440, while the sum is 26.

The square root of 20631581 is about 4542.2000176126. The cubic root of 20631581 is about 274.2694926103.

It can be divided in two parts, 20631 and 581, that added together give a palindrome (21212).

The spelling of 20631581 in words is "twenty million, six hundred thirty-one thousand, five hundred eighty-one".