21549391 has 2 divisors, whose sum is σ = 21549392. Its totient is φ = 21549390.

The previous prime is 21549389. The next prime is 21549397. The reversal of 21549391 is 19394512.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21549391 - 2¹ = 21549389 is a prime.

Together with 21549389, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21549397) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10774695 + 10774696.

It is an arithmetic number, because the mean of its divisors is an integer number (10774696).

Almost surely, 2^21549391 is an apocalyptic number.

21549391 is a deficient number, since it is larger than the sum of its proper divisors (1).

21549391 is an equidigital number, since it uses as much as digits as its factorization.

21549391 is an evil number, because the sum of its binary digits is even.

The product of its digits is 9720, while the sum is 34.

The square root of 21549391 is about 4642.1321609795. The cubic root of 21549391 is about 278.2776542104.

The spelling of 21549391 in words is "twenty-one million, five hundred forty-nine thousand, three hundred ninety-one".