21256017 has 4 divisors (see below), whose sum is σ = 28341360. Its totient is φ = 14170676.

The previous prime is 21256013. The next prime is 21256033. The reversal of 21256017 is 71065212.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21256017 - 2² = 21256013 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21256013) 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 in 3 ways as a sum of consecutive naturals, for example, 3542667 + ... + 3542672.

It is an arithmetic number, because the mean of its divisors is an integer number (7085340).

Almost surely, 2^21256017 is an apocalyptic number.

It is an amenable number.

21256017 is a deficient number, since it is larger than the sum of its proper divisors (7085343).

21256017 is an equidigital number, since it uses as much as digits as its factorization.

21256017 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7085342.

The product of its (nonzero) digits is 840, while the sum is 24.

The square root of 21256017 is about 4610.4248177364. The cubic root of 21256017 is about 277.0090532128.

The spelling of 21256017 in words is "twenty-one million, two hundred fifty-six thousand, seventeen".