21565541 has 8 divisors (see below), whose sum is σ = 22179960. Its totient is φ = 20958912.

The previous prime is 21565519. The next prime is 21565547. The reversal of 21565541 is 14556512.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 7540516 + 14025025 = 2746^2 + 3745^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21565541 - 2⁶ = 21565477 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 (21565547) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3911 + ... + 7643.

It is an arithmetic number, because the mean of its divisors is an integer number (2772495).

Almost surely, 2^21565541 is an apocalyptic number.

It is an amenable number.

21565541 is a deficient number, since it is larger than the sum of its proper divisors (614419).

21565541 is a wasteful number, since it uses less digits than its factorization.

21565541 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3895.

The product of its digits is 6000, while the sum is 29.

The square root of 21565541 is about 4643.8713375803. The cubic root of 21565541 is about 278.3471544246.

It can be divided in two parts, 215 and 65541, that added together give a palindrome (65756).

The spelling of 21565541 in words is "twenty-one million, five hundred sixty-five thousand, five hundred forty-one".