21785891 has 4 divisors (see below), whose sum is σ = 23067432. Its totient is φ = 20504352.

The previous prime is 21785867. The next prime is 21785903. The reversal of 21785891 is 19858712.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21785891 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21785851) 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, 640745 + ... + 640778.

It is an arithmetic number, because the mean of its divisors is an integer number (5766858).

Almost surely, 2^21785891 is an apocalyptic number.

21785891 is a deficient number, since it is larger than the sum of its proper divisors (1281541).

21785891 is a wasteful number, since it uses less digits than its factorization.

21785891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1281540.

The product of its digits is 40320, while the sum is 41.

The square root of 21785891 is about 4667.5358595302. The cubic root of 21785891 is about 279.2919653571.

The spelling of 21785891 in words is "twenty-one million, seven hundred eighty-five thousand, eight hundred ninety-one".