21897845 has 4 divisors (see below), whose sum is σ = 26277420. Its totient is φ = 17518272.

The previous prime is 21897809. The next prime is 21897857. The reversal of 21897845 is 54879812.

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 8421604 + 13476241 = 2902^2 + 3671^2 .

It is a cyclic number.

It is not a de Polignac number, because 21897845 - 2⁶ = 21897781 is a prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21897796 and 21897805.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2189780 + ... + 2189789.

It is an arithmetic number, because the mean of its divisors is an integer number (6569355).

Almost surely, 2^21897845 is an apocalyptic number.

It is an amenable number.

21897845 is a deficient number, since it is larger than the sum of its proper divisors (4379575).

21897845 is an equidigital number, since it uses as much as digits as its factorization.

21897845 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4379574.

The product of its digits is 161280, while the sum is 44.

The square root of 21897845 is about 4679.5133293966. The cubic root of 21897845 is about 279.7695595488.

The spelling of 21897845 in words is "twenty-one million, eight hundred ninety-seven thousand, eight hundred forty-five".