21545391 has 16 divisors (see below), whose sum is σ = 33323264. Its totient is φ = 12127104.

The previous prime is 21545369. The next prime is 21545393. The reversal of 21545391 is 19354512.

It is not a de Polignac number, because 21545391 - 2⁶ = 21545327 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 (21545393) 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, 6250 + ... + 9063.

It is an arithmetic number, because the mean of its divisors is an integer number (2082704).

Almost surely, 2^21545391 is an apocalyptic number.

21545391 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21545391 is a deficient number, since it is larger than the sum of its proper divisors (11777873).

21545391 is a wasteful number, since it uses less digits than its factorization.

21545391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15390.

The product of its digits is 5400, while the sum is 30.

The square root of 21545391 is about 4641.7013044788. The cubic root of 21545391 is about 278.2604351701.

The spelling of 21545391 in words is "twenty-one million, five hundred forty-five thousand, three hundred ninety-one".