21897855 has 36 divisors (see below), whose sum is σ = 44157672. Its totient is φ = 10009440.

The previous prime is 21897809. The next prime is 21897857. The reversal of 21897855 is 55879812.

It is a happy number.

It is not a de Polignac number, because 21897855 - 2¹¹ = 21895807 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a self number, because there is not a number n which added to its sum of digits gives 21897855.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21897857) by changing a digit.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 2761 + ... + 7170.

It is an arithmetic number, because the mean of its divisors is an integer number (1226602).

Almost surely, 2^21897855 is an apocalyptic number.

21897855 is an abundant number, since it is smaller than the sum of its proper divisors (22259817).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21897855 is a wasteful number, since it uses less digits than its factorization.

21897855 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9956 (or 9946 counting only the distinct ones).

The product of its digits is 201600, while the sum is 45.

The square root of 21897855 is about 4679.5143978836. The cubic root of 21897855 is about 279.7696021359.

The spelling of 21897855 in words is "twenty-one million, eight hundred ninety-seven thousand, eight hundred fifty-five".