21051257 has 2 divisors, whose sum is σ = 21051258. Its totient is φ = 21051256.

The previous prime is 21051241. The next prime is 21051271. The reversal of 21051257 is 75215012.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18567481 + 2483776 = 4309^2 + 1576^2 .

It is a cyclic number.

It is not a de Polignac number, because 21051257 - 2⁴ = 21051241 is a prime.

It is not a weakly prime, because it can be changed into another prime (21071257) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10525628 + 10525629.

It is an arithmetic number, because the mean of its divisors is an integer number (10525629).

Almost surely, 2^21051257 is an apocalyptic number.

It is an amenable number.

21051257 is a deficient number, since it is larger than the sum of its proper divisors (1).

21051257 is an equidigital number, since it uses as much as digits as its factorization.

21051257 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 700, while the sum is 23.

The square root of 21051257 is about 4588.1648836981. The cubic root of 21051257 is about 276.1167022052.

Adding to 21051257 its reverse (75215012), we get a palindrome (96266269).

The spelling of 21051257 in words is "twenty-one million, fifty-one thousand, two hundred fifty-seven".