21256693 has 2 divisors, whose sum is σ = 21256694. Its totient is φ = 21256692.

The previous prime is 21256691. The next prime is 21256709. The reversal of 21256693 is 39665212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14085009 + 7171684 = 3753^2 + 2678^2 .

It is a cyclic number.

It is not a de Polignac number, because 21256693 - 2¹ = 21256691 is a prime.

Together with 21256691, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21256691) 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, 10628346 + 10628347.

It is an arithmetic number, because the mean of its divisors is an integer number (10628347).

Almost surely, 2^21256693 is an apocalyptic number.

It is an amenable number.

21256693 is a deficient number, since it is larger than the sum of its proper divisors (1).

21256693 is an equidigital number, since it uses as much as digits as its factorization.

21256693 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 19440, while the sum is 34.

The square root of 21256693 is about 4610.4981292698. The cubic root of 21256693 is about 277.0119897324.

The spelling of 21256693 in words is "twenty-one million, two hundred fifty-six thousand, six hundred ninety-three".