21945891 has 12 divisors (see below), whose sum is σ = 32163656. Its totient is φ = 13300320.

The previous prime is 21945881. The next prime is 21945907. The reversal of 21945891 is 19854912.

It is not a de Polignac number, because 21945891 - 2¹¹ = 21943843 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21945811) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 29866 + ... + 30591.

Almost surely, 2^21945891 is an apocalyptic number.

21945891 is a deficient number, since it is larger than the sum of its proper divisors (10217765).

21945891 is a wasteful number, since it uses less digits than its factorization.

21945891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 60482 (or 60471 counting only the distinct ones).

The product of its digits is 25920, while the sum is 39.

The square root of 21945891 is about 4684.6441700518. The cubic root of 21945891 is about 279.9740239508.

The spelling of 21945891 in words is "twenty-one million, nine hundred forty-five thousand, eight hundred ninety-one".