21615841 has 4 divisors (see below), whose sum is σ = 23278612. Its totient is φ = 19953072.

The previous prime is 21615809. The next prime is 21615851. The reversal of 21615841 is 14851612.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 1679616 + 19936225 = 1296^2 + 4465^2 .

It is a cyclic number.

It is not a de Polignac number, because 21615841 - 2⁵ = 21615809 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21615851) 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, 831366 + ... + 831391.

It is an arithmetic number, because the mean of its divisors is an integer number (5819653).

Almost surely, 2^21615841 is an apocalyptic number.

It is an amenable number.

21615841 is a deficient number, since it is larger than the sum of its proper divisors (1662771).

21615841 is a wasteful number, since it uses less digits than its factorization.

21615841 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1662770.

The product of its digits is 1920, while the sum is 28.

The square root of 21615841 is about 4649.2839233585. The cubic root of 21615841 is about 278.5633943145.

The spelling of 21615841 in words is "twenty-one million, six hundred fifteen thousand, eight hundred forty-one".