21256818 has 16 divisors (see below), whose sum is σ = 46378656. Its totient is φ = 6441440.

The previous prime is 21256813. The next prime is 21256841. The reversal of 21256818 is 81865212.

It is a super-2 number, since 2×21256818² = 903704622970248, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (33).

It is not an unprimeable number, because it can be changed into a prime (21256813) 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 7 ways as a sum of consecutive naturals, for example, 160971 + ... + 161102.

It is an arithmetic number, because the mean of its divisors is an integer number (2898666).

Almost surely, 2^21256818 is an apocalyptic number.

21256818 is an abundant number, since it is smaller than the sum of its proper divisors (25121838).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21256818 is a wasteful number, since it uses less digits than its factorization.

21256818 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 322089.

The product of its digits is 7680, while the sum is 33.

The square root of 21256818 is about 4610.5116852688. The cubic root of 21256818 is about 277.0125327211.

The spelling of 21256818 in words is "twenty-one million, two hundred fifty-six thousand, eight hundred eighteen".