20720981 has 4 divisors (see below), whose sum is σ = 20800032. Its totient is φ = 20641932.

The previous prime is 20720971. The next prime is 20721013. The reversal of 20720981 is 18902702.

It is a happy number.

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 a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20720981 is a prime.

It is a super-2 number, since 2×20720981² = 858718107204722, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20720911) 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 3 ways as a sum of consecutive naturals, for example, 39131 + ... + 39656.

It is an arithmetic number, because the mean of its divisors is an integer number (5200008).

Almost surely, 2^20720981 is an apocalyptic number.

It is an amenable number.

20720981 is a deficient number, since it is larger than the sum of its proper divisors (79051).

20720981 is an equidigital number, since it uses as much as digits as its factorization.

20720981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 79050.

The product of its (nonzero) digits is 2016, while the sum is 29.

The square root of 20720981 is about 4552.0304260846. The cubic root of 20720981 is about 274.6650732449.

The spelling of 20720981 in words is "twenty million, seven hundred twenty thousand, nine hundred eighty-one".