21256999 has 2 divisors, whose sum is σ = 21257000. Its totient is φ = 21256998.

The previous prime is 21256997. The next prime is 21257003. The reversal of 21256999 is 99965212.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21256999 - 2¹ = 21256997 is a prime.

Together with 21256997, 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 (21256997) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10628499 + 10628500.

It is an arithmetic number, because the mean of its divisors is an integer number (10628500).

Almost surely, 2^21256999 is an apocalyptic number.

21256999 is a deficient number, since it is larger than the sum of its proper divisors (1).

21256999 is an equidigital number, since it uses as much as digits as its factorization.

21256999 is an evil number, because the sum of its binary digits is even.

The product of its digits is 87480, while the sum is 43.

The square root of 21256999 is about 4610.5313142847. The cubic root of 21256999 is about 277.0133189649.

The spelling of 21256999 in words is "twenty-one million, two hundred fifty-six thousand, nine hundred ninety-nine".