21405541 has 4 divisors (see below), whose sum is σ = 21462400. Its totient is φ = 21348684.

The previous prime is 21405523. The next prime is 21405551. The reversal of 21405541 is 14550412.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21405541 - 2¹³ = 21397349 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 (21405511) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 27861 + ... + 28618.

It is an arithmetic number, because the mean of its divisors is an integer number (5365600).

Almost surely, 2^21405541 is an apocalyptic number.

It is an amenable number.

21405541 is a deficient number, since it is larger than the sum of its proper divisors (56859).

21405541 is an equidigital number, since it uses as much as digits as its factorization.

21405541 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 56858.

The product of its (nonzero) digits is 800, while the sum is 22.

The square root of 21405541 is about 4626.6122595264. The cubic root of 21405541 is about 277.6570698593.

Adding to 21405541 its reverse (14550412), we get a palindrome (35955953).

The spelling of 21405541 in words is "twenty-one million, four hundred five thousand, five hundred forty-one".