21331657 has 2 divisors, whose sum is σ = 21331658. Its totient is φ = 21331656.

The previous prime is 21331643. The next prime is 21331663. The reversal of 21331657 is 75613312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12187081 + 9144576 = 3491^2 + 3024^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21331657 is a prime.

It is not a weakly prime, because it can be changed into another prime (21331637) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10665828 + 10665829.

It is an arithmetic number, because the mean of its divisors is an integer number (10665829).

Almost surely, 2^21331657 is an apocalyptic number.

It is an amenable number.

21331657 is a deficient number, since it is larger than the sum of its proper divisors (1).

21331657 is an equidigital number, since it uses as much as digits as its factorization.

21331657 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3780, while the sum is 28.

The square root of 21331657 is about 4618.6206815455. The cubic root of 21331657 is about 277.3372451461.

Adding to 21331657 its reverse (75613312), we get a palindrome (96944969).

The spelling of 21331657 in words is "twenty-one million, three hundred thirty-one thousand, six hundred fifty-seven".