21921685 has 4 divisors (see below), whose sum is σ = 26306028. Its totient is φ = 17537344.

The previous prime is 21921667. The next prime is 21921689. The reversal of 21921685 is 58612912.

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 4231249 + 17690436 = 2057^2 + 4206^2 .

It is a cyclic number.

It is not a de Polignac number, because 21921685 - 2¹⁵ = 21888917 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21921685.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21921689) 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, 2192164 + ... + 2192173.

It is an arithmetic number, because the mean of its divisors is an integer number (6576507).

Almost surely, 2^21921685 is an apocalyptic number.

It is an amenable number.

21921685 is a deficient number, since it is larger than the sum of its proper divisors (4384343).

21921685 is an equidigital number, since it uses as much as digits as its factorization.

21921685 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4384342.

The product of its digits is 8640, while the sum is 34.

The square root of 21921685 is about 4682.0599099114. The cubic root of 21921685 is about 279.8710503172.

It can be divided in two parts, 219 and 21685, that added together give a square (21904 = 148²).

The spelling of 21921685 in words is "twenty-one million, nine hundred twenty-one thousand, six hundred eighty-five".