21920391 has 12 divisors (see below), whose sum is σ = 32519032. Its totient is φ = 14218416.

The previous prime is 21920389. The next prime is 21920399. The reversal of 21920391 is 19302912.

It is not a de Polignac number, because 21920391 - 2¹ = 21920389 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21920399) 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, 32581 + ... + 33246.

Almost surely, 2^21920391 is an apocalyptic number.

21920391 is a deficient number, since it is larger than the sum of its proper divisors (10598641).

21920391 is a wasteful number, since it uses less digits than its factorization.

21920391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 65870 (or 65867 counting only the distinct ones).

The product of its (nonzero) digits is 972, while the sum is 27.

The square root of 21920391 is about 4681.9217208322. The cubic root of 21920391 is about 279.8655434372.

The spelling of 21920391 in words is "twenty-one million, nine hundred twenty thousand, three hundred ninety-one".