21231657 has 24 divisors (see below), whose sum is σ = 32722560. Its totient is φ = 13219200.

The previous prime is 21231631. The next prime is 21231677. The reversal of 21231657 is 75613212.

It is a happy number.

21231657 is a `hidden beast` number, since 2 + 1 + 2 + 3 + 1 + 657 = 666.

It is not a de Polignac number, because 21231657 - 2¹² = 21227561 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21231657.

It is not an unprimeable number, because it can be changed into a prime (21231677) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 22644 + ... + 23562.

It is an arithmetic number, because the mean of its divisors is an integer number (1363440).

Almost surely, 2^21231657 is an apocalyptic number.

It is an amenable number.

21231657 is a deficient number, since it is larger than the sum of its proper divisors (11490903).

21231657 is a wasteful number, since it uses less digits than its factorization.

21231657 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1093 (or 1090 counting only the distinct ones).

The product of its digits is 2520, while the sum is 27.

The square root of 21231657 is about 4607.7822214163. The cubic root of 21231657 is about 276.9031926784.

Adding to 21231657 its reverse (75613212), we get a palindrome (96844869).

The spelling of 21231657 in words is "twenty-one million, two hundred thirty-one thousand, six hundred fifty-seven".