21557051 has 4 divisors (see below), whose sum is σ = 22139712. Its totient is φ = 20974392.

The previous prime is 21557047. The next prime is 21557057. The reversal of 21557051 is 15075512.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 21557051 - 2² = 21557047 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21557051.

It is not an unprimeable number, because it can be changed into a prime (21557057) 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, 291275 + ... + 291348.

It is an arithmetic number, because the mean of its divisors is an integer number (5534928).

Almost surely, 2^21557051 is an apocalyptic number.

21557051 is a deficient number, since it is larger than the sum of its proper divisors (582661).

21557051 is an equidigital number, since it uses as much as digits as its factorization.

21557051 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 582660.

The product of its (nonzero) digits is 1750, while the sum is 26.

The square root of 21557051 is about 4642.9571395825. The cubic root of 21557051 is about 278.3106227262.

The spelling of 21557051 in words is "twenty-one million, five hundred fifty-seven thousand, fifty-one".