21685157 has 4 divisors (see below), whose sum is σ = 23353260. Its totient is φ = 20017056.

The previous prime is 21685133. The next prime is 21685163. The reversal of 21685157 is 75158612.

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 4661281 + 17023876 = 2159^2 + 4126^2 .

It is a cyclic number.

It is not a de Polignac number, because 21685157 - 2⁶ = 21685093 is a prime.

It is a super-2 number, since 2×21685157² = 940492068229298, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21685177) 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 3 ways as a sum of consecutive naturals, for example, 834032 + ... + 834057.

It is an arithmetic number, because the mean of its divisors is an integer number (5838315).

Almost surely, 2^21685157 is an apocalyptic number.

It is an amenable number.

21685157 is a deficient number, since it is larger than the sum of its proper divisors (1668103).

21685157 is a wasteful number, since it uses less digits than its factorization.

21685157 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1668102.

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

The square root of 21685157 is about 4656.7324380943. The cubic root of 21685157 is about 278.8608350896.

It can be divided in two parts, 2 and 1685157, that added together give a cube (1685159 = 119³).

The spelling of 21685157 in words is "twenty-one million, six hundred eighty-five thousand, one hundred fifty-seven".