21157 has 2 divisors, whose sum is σ = 21158. Its totient is φ = 21156.

The previous prime is 21149. The next prime is 21163. The reversal of 21157 is 75112.

21157 is nontrivially palindromic in base 2.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12321 + 8836 = 111^2 + 94^2 .

It is a cyclic number.

It is not a de Polignac number, because 21157 - 2³ = 21149 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21157.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21107) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10578 + 10579.

It is an arithmetic number, because the mean of its divisors is an integer number (10579).

2²¹¹⁵⁷ is an apocalyptic number.

It is an amenable number.

21157 is a deficient number, since it is larger than the sum of its proper divisors (1).

21157 is an equidigital number, since it uses as much as digits as its factorization.

21157 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 70, while the sum is 16.

The square root of 21157 is about 145.4544602272. The cubic root of 21157 is about 27.6578252744.

Adding to 21157 its reverse (75112), we get a palindrome (96269).

The spelling of 21157 in words is "twenty-one thousand, one hundred fifty-seven".