21660557 has 4 divisors (see below), whose sum is σ = 21677340. Its totient is φ = 21643776.

The previous prime is 21660523. The next prime is 21660559. The reversal of 21660557 is 75506612.

It is a happy number.

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 306916 + 21353641 = 554^2 + 4621^2 .

It is a cyclic number.

It is not a de Polignac number, because 21660557 - 2¹² = 21656461 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 (21660559) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 6278 + ... + 9095.

It is an arithmetic number, because the mean of its divisors is an integer number (5419335).

Almost surely, 2^21660557 is an apocalyptic number.

It is an amenable number.

21660557 is a deficient number, since it is larger than the sum of its proper divisors (16783).

21660557 is a wasteful number, since it uses less digits than its factorization.

21660557 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16782.

The product of its (nonzero) digits is 12600, while the sum is 32.

The square root of 21660557 is about 4654.0903515080. The cubic root of 21660557 is about 278.7553470792.

The spelling of 21660557 in words is "twenty-one million, six hundred sixty thousand, five hundred fifty-seven".