20981599 has 4 divisors (see below), whose sum is σ = 21428064. Its totient is φ = 20535136.

The previous prime is 20981593. The next prime is 20981617. The reversal of 20981599 is 99518902.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 20981599 - 2¹¹ = 20979551 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20981593) 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, 223162 + ... + 223255.

It is an arithmetic number, because the mean of its divisors is an integer number (5357016).

Almost surely, 2^20981599 is an apocalyptic number.

20981599 is a deficient number, since it is larger than the sum of its proper divisors (446465).

20981599 is an equidigital number, since it uses as much as digits as its factorization.

20981599 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 446464.

The product of its (nonzero) digits is 58320, while the sum is 43.

The square root of 20981599 is about 4580.5675412551. The cubic root of 20981599 is about 275.8118116080.

The spelling of 20981599 in words is "twenty million, nine hundred eighty-one thousand, five hundred ninety-nine".