21157685 has 4 divisors (see below), whose sum is σ = 25389228. Its totient is φ = 16926144.

The previous prime is 21157649. The next prime is 21157693. The reversal of 21157685 is 58675112.

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 13126129 + 8031556 = 3623^2 + 2834^2 .

It is a cyclic number.

It is not a de Polignac number, because 21157685 - 2⁸ = 21157429 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

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 3 ways as a sum of consecutive naturals, for example, 2115764 + ... + 2115773.

It is an arithmetic number, because the mean of its divisors is an integer number (6347307).

Almost surely, 2^21157685 is an apocalyptic number.

It is an amenable number.

21157685 is a deficient number, since it is larger than the sum of its proper divisors (4231543).

21157685 is an equidigital number, since it uses as much as digits as its factorization.

21157685 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4231542.

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

The square root of 21157685 is about 4599.7483626825. The cubic root of 21157685 is about 276.5812376358.

The spelling of 21157685 in words is "twenty-one million, one hundred fifty-seven thousand, six hundred eighty-five".