21666853 has 6 divisors (see below), whose sum is σ = 23351622. Its totient is φ = 19984680.

The previous prime is 21666829. The next prime is 21666863. The reversal of 21666853 is 35866612.

It can be written as a sum of positive squares in only one way, i.e., 15000129 + 6666724 = 3873^2 + 2582^2 .

It is not a de Polignac number, because 21666853 - 2⁹ = 21666341 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21666863) 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 5 ways as a sum of consecutive naturals, for example, 16138 + ... + 17428.

It is an arithmetic number, because the mean of its divisors is an integer number (3891937).

Almost surely, 2^21666853 is an apocalyptic number.

It is an amenable number.

21666853 is a deficient number, since it is larger than the sum of its proper divisors (1684769).

21666853 is an frugal number, since it uses more digits than its factorization.

21666853 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2595 (or 1304 counting only the distinct ones).

The product of its digits is 51840, while the sum is 37.

The square root of 21666853 is about 4654.7666966240. The cubic root of 21666853 is about 278.7823527505.

The spelling of 21666853 in words is "twenty-one million, six hundred sixty-six thousand, eight hundred fifty-three".