21747891 has 16 divisors (see below), whose sum is σ = 31852800. Its totient is φ = 13089120.

The previous prime is 21747881. The next prime is 21747899. The reversal of 21747891 is 19874712.

It is not a de Polignac number, because 21747891 - 2⁶ = 21747827 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21747899) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2706 + ... + 7128.

It is an arithmetic number, because the mean of its divisors is an integer number (1990800).

Almost surely, 2^21747891 is an apocalyptic number.

21747891 is a deficient number, since it is larger than the sum of its proper divisors (10104909).

21747891 is a wasteful number, since it uses less digits than its factorization.

21747891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4586.

The product of its digits is 28224, while the sum is 39.

The square root of 21747891 is about 4663.4634125294. The cubic root of 21747891 is about 279.1294860213.

The spelling of 21747891 in words is "twenty-one million, seven hundred forty-seven thousand, eight hundred ninety-one".