21731157 has 18 divisors (see below), whose sum is σ = 36514998. Its totient is φ = 12417552.

The previous prime is 21731147. The next prime is 21731161. The reversal of 21731157 is 75113712.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 20196036 + 1535121 = 4494^2 + 1239^2 .

It is not a de Polignac number, because 21731157 - 2⁴ = 21731141 is a prime.

It is a zygodrome in base 3.

It is a self number, because there is not a number n which added to its sum of digits gives 21731157.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21731147) by changing a digit.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 24198 + ... + 25079.

It is an arithmetic number, because the mean of its divisors is an integer number (2028611).

Almost surely, 2^21731157 is an apocalyptic number.

It is an amenable number.

21731157 is a deficient number, since it is larger than the sum of its proper divisors (14783841).

21731157 is a wasteful number, since it uses less digits than its factorization.

21731157 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 49297 (or 49287 counting only the distinct ones).

The product of its digits is 1470, while the sum is 27.

The square root of 21731157 is about 4661.6689071619. The cubic root of 21731157 is about 279.0578752253.

Adding to 21731157 its reverse (75113712), we get a palindrome (96844869).

The spelling of 21731157 in words is "twenty-one million, seven hundred thirty-one thousand, one hundred fifty-seven".