21685557 has 8 divisors (see below), whose sum is σ = 30614976. Its totient is φ = 13606592.

The previous prime is 21685553. The next prime is 21685571. The reversal of 21685557 is 75558612.

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 21685557 - 2² = 21685553 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21685553) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 212553 + ... + 212654.

It is an arithmetic number, because the mean of its divisors is an integer number (3826872).

Almost surely, 2^21685557 is an apocalyptic number.

It is an amenable number.

21685557 is a deficient number, since it is larger than the sum of its proper divisors (8929419).

21685557 is a wasteful number, since it uses less digits than its factorization.

21685557 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 425227.

The product of its digits is 84000, while the sum is 39.

The square root of 21685557 is about 4656.7753864665. The cubic root of 21685557 is about 278.8625496825.

The spelling of 21685557 in words is "twenty-one million, six hundred eighty-five thousand, five hundred fifty-seven".