21557861 has 8 divisors (see below), whose sum is σ = 23261280. Its totient is φ = 19860912.

The previous prime is 21557843. The next prime is 21557917. The reversal of 21557861 is 16875512.

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 21557861 - 2¹⁴ = 21541477 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 (21550861) 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, 7070 + ... + 9648.

It is an arithmetic number, because the mean of its divisors is an integer number (2907660).

Almost surely, 2^21557861 is an apocalyptic number.

It is an amenable number.

21557861 is a deficient number, since it is larger than the sum of its proper divisors (1703419).

21557861 is a wasteful number, since it uses less digits than its factorization.

21557861 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3235.

The product of its digits is 16800, while the sum is 35.

The square root of 21557861 is about 4643.0443676536. The cubic root of 21557861 is about 278.3141084964.

The spelling of 21557861 in words is "twenty-one million, five hundred fifty-seven thousand, eight hundred sixty-one".