21856766 has 4 divisors (see below), whose sum is σ = 32785152. Its totient is φ = 10928382.

The previous prime is 21856763. The next prime is 21856801. The reversal of 21856766 is 66765812.

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

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21856763) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5464190 + ... + 5464193.

It is an arithmetic number, because the mean of its divisors is an integer number (8196288).

Almost surely, 2^21856766 is an apocalyptic number.

21856766 is a deficient number, since it is larger than the sum of its proper divisors (10928386).

21856766 is a wasteful number, since it uses less digits than its factorization.

21856766 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10928385.

The product of its digits is 120960, while the sum is 41.

The square root of 21856766 is about 4675.1220304929. The cubic root of 21856766 is about 279.5945065891.

It can be divided in two parts, 21856 and 766, that added together give a palindrome (22622).

The spelling of 21856766 in words is "twenty-one million, eight hundred fifty-six thousand, seven hundred sixty-six".