21157931 has 8 divisors (see below), whose sum is σ = 21744240. Its totient is φ = 20579328.

The previous prime is 21157921. The next prime is 21157933. The reversal of 21157931 is 13975112.

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 21157931 - 2⁶ = 21157867 is a prime.

It is a super-2 number, since 2×21157931² = 895316088401522, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21157894 and 21157903.

It is not an unprimeable number, because it can be changed into a prime (21157933) 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 7 ways as a sum of consecutive naturals, for example, 3875 + ... + 7571.

It is an arithmetic number, because the mean of its divisors is an integer number (2718030).

Almost surely, 2^21157931 is an apocalyptic number.

21157931 is a deficient number, since it is larger than the sum of its proper divisors (586309).

21157931 is an equidigital number, since it uses as much as digits as its factorization.

21157931 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3853.

The product of its digits is 1890, while the sum is 29.

The square root of 21157931 is about 4599.7751031980. The cubic root of 21157931 is about 276.5823095666.

The spelling of 21157931 in words is "twenty-one million, one hundred fifty-seven thousand, nine hundred thirty-one".