21257993 has 2 divisors, whose sum is σ = 21257994. Its totient is φ = 21257992.

The previous prime is 21257969. The next prime is 21258001. The reversal of 21257993 is 39975212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20720704 + 537289 = 4552^2 + 733^2 .

It is a cyclic number.

It is not a de Polignac number, because 21257993 - 2⁸ = 21257737 is a prime.

It is not a weakly prime, because it can be changed into another prime (21257923) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10628996 + 10628997.

It is an arithmetic number, because the mean of its divisors is an integer number (10628997).

Almost surely, 2^21257993 is an apocalyptic number.

It is an amenable number.

21257993 is a deficient number, since it is larger than the sum of its proper divisors (1).

21257993 is an equidigital number, since it uses as much as digits as its factorization.

21257993 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 34020, while the sum is 38.

The square root of 21257993 is about 4610.6391097114. The cubic root of 21257993 is about 277.0176367106.

The spelling of 21257993 in words is "twenty-one million, two hundred fifty-seven thousand, nine hundred ninety-three".