20581981 has 8 divisors (see below), whose sum is σ = 23567040. Its totient is φ = 17608128.

The previous prime is 20581961. The next prime is 20581991. The reversal of 20581981 is 18918502.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 20581981 - 2⁹ = 20581469 is a prime.

It is a super-2 number, since 2×20581981² = 847235883768722, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20581901) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1605 + ... + 6613.

It is an arithmetic number, because the mean of its divisors is an integer number (2945880).

Almost surely, 2^20581981 is an apocalyptic number.

It is an amenable number.

20581981 is a deficient number, since it is larger than the sum of its proper divisors (2985059).

20581981 is an equidigital number, since it uses as much as digits as its factorization.

20581981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5603.

The product of its (nonzero) digits is 5760, while the sum is 34.

The square root of 20581981 is about 4536.7368228717. The cubic root of 20581981 is about 274.0495275167.

The spelling of 20581981 in words is "twenty million, five hundred eighty-one thousand, nine hundred eighty-one".