20969581 has 4 divisors (see below), whose sum is σ = 21692700. Its totient is φ = 20246464.

The previous prime is 20969527. The next prime is 20969623. The reversal of 20969581 is 18596902.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 18596902 = 2 ⋅9298451.

It can be written as a sum of positive squares in 2 ways, for example, as 12320100 + 8649481 = 3510^2 + 2941^2 .

It is a cyclic number.

It is not a de Polignac number, because 20969581 - 2⁷ = 20969453 is a prime.

It is a super-2 number, since 2×20969581² = 879446654631122, which contains 22 as substring.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20969281) 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, 361516 + ... + 361573.

It is an arithmetic number, because the mean of its divisors is an integer number (5423175).

Almost surely, 2^20969581 is an apocalyptic number.

It is an amenable number.

20969581 is a deficient number, since it is larger than the sum of its proper divisors (723119).

20969581 is an equidigital number, since it uses as much as digits as its factorization.

20969581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 723118.

The product of its (nonzero) digits is 38880, while the sum is 40.

The square root of 20969581 is about 4579.2555071758. The cubic root of 20969581 is about 275.7591410207.

The spelling of 20969581 in words is "twenty million, nine hundred sixty-nine thousand, five hundred eighty-one".