21120257 has 2 divisors, whose sum is σ = 21120258. Its totient is φ = 21120256.

The previous prime is 21120251. The next prime is 21120259. The reversal of 21120257 is 75202112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20421361 + 698896 = 4519^2 + 836^2 .

It is a cyclic number.

It is not a de Polignac number, because 21120257 - 2⁶ = 21120193 is a prime.

Together with 21120259, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21120251) 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, 10560128 + 10560129.

It is an arithmetic number, because the mean of its divisors is an integer number (10560129).

Almost surely, 2^21120257 is an apocalyptic number.

It is an amenable number.

21120257 is a deficient number, since it is larger than the sum of its proper divisors (1).

21120257 is an equidigital number, since it uses as much as digits as its factorization.

21120257 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 280, while the sum is 20.

The square root of 21120257 is about 4595.6780783688. The cubic root of 21120257 is about 276.4180503946.

Adding to 21120257 its reverse (75202112), we get a palindrome (96322369).

The spelling of 21120257 in words is "twenty-one million, one hundred twenty thousand, two hundred fifty-seven".