20815581 has 4 divisors (see below), whose sum is σ = 27754112. Its totient is φ = 13877052.

The previous prime is 20815559. The next prime is 20815603. The reversal of 20815581 is 18551802.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is an interprime number because it is at equal distance from previous prime (20815559) and next prime (20815603).

It is not a de Polignac number, because 20815581 - 2⁶ = 20815517 is a prime.

It is a super-2 number, since 2×20815581² = 866576824735122, 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 (20815481) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3469261 + ... + 3469266.

It is an arithmetic number, because the mean of its divisors is an integer number (6938528).

Almost surely, 2^20815581 is an apocalyptic number.

It is an amenable number.

20815581 is a deficient number, since it is larger than the sum of its proper divisors (6938531).

20815581 is an equidigital number, since it uses as much as digits as its factorization.

20815581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6938530.

The product of its (nonzero) digits is 3200, while the sum is 30.

The square root of 20815581 is about 4562.4095607475. The cubic root of 20815581 is about 275.0824259806.

The spelling of 20815581 in words is "twenty million, eight hundred fifteen thousand, five hundred eighty-one".