21256547 has 4 divisors (see below), whose sum is σ = 22891680. Its totient is φ = 19621416.

The previous prime is 21256541. The next prime is 21256559. The reversal of 21256547 is 74565212.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21256547 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21256541) 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, 817547 + ... + 817572.

It is an arithmetic number, because the mean of its divisors is an integer number (5722920).

Almost surely, 2^21256547 is an apocalyptic number.

21256547 is a deficient number, since it is larger than the sum of its proper divisors (1635133).

21256547 is a wasteful number, since it uses less digits than its factorization.

21256547 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1635132.

The product of its digits is 16800, while the sum is 32.

The square root of 21256547 is about 4610.4822958124. The cubic root of 21256547 is about 277.0113555190.

The spelling of 21256547 in words is "twenty-one million, two hundred fifty-six thousand, five hundred forty-seven".