21985813 has 4 divisors (see below), whose sum is σ = 22034380. Its totient is φ = 21937248.

The previous prime is 21985783. The next prime is 21985823. The reversal of 21985813 is 31858912.

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

It can be written as a sum of positive squares in 2 ways, for example, as 15944049 + 6041764 = 3993^2 + 2458^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21985813 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 12.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21985823) 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, 23598 + ... + 24511.

It is an arithmetic number, because the mean of its divisors is an integer number (5508595).

Almost surely, 2^21985813 is an apocalyptic number.

It is an amenable number.

21985813 is a deficient number, since it is larger than the sum of its proper divisors (48567).

21985813 is an equidigital number, since it uses as much as digits as its factorization.

21985813 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 48566.

The product of its digits is 17280, while the sum is 37.

The square root of 21985813 is about 4688.9031766502. The cubic root of 21985813 is about 280.1436890049.

The spelling of 21985813 in words is "twenty-one million, nine hundred eighty-five thousand, eight hundred thirteen".