21256997 has 2 divisors, whose sum is σ = 21256998. Its totient is φ = 21256996.

The previous prime is 21256931. The next prime is 21256999. The reversal of 21256997 is 79965212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20802721 + 454276 = 4561^2 + 674^2 .

It is a cyclic number.

It is not a de Polignac number, because 21256997 - 2¹⁰ = 21255973 is a prime.

Together with 21256999, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21256999) 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, 10628498 + 10628499.

It is an arithmetic number, because the mean of its divisors is an integer number (10628499).

Almost surely, 2^21256997 is an apocalyptic number.

It is an amenable number.

21256997 is a deficient number, since it is larger than the sum of its proper divisors (1).

21256997 is an equidigital number, since it uses as much as digits as its factorization.

21256997 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 68040, while the sum is 41.

The square root of 21256997 is about 4610.5310973900. The cubic root of 21256997 is about 277.0133102772.

The spelling of 21256997 in words is "twenty-one million, two hundred fifty-six thousand, nine hundred ninety-seven".