21666418 has 4 divisors (see below), whose sum is σ = 32499630. Its totient is φ = 10833208.

The previous prime is 21666397. The next prime is 21666443. The reversal of 21666418 is 81466612.

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

It can be written as a sum of positive squares in only one way, i.e., 12981609 + 8684809 = 3603^2 + 2947^2 .

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5416603 + ... + 5416606.

Almost surely, 2^21666418 is an apocalyptic number.

21666418 is a deficient number, since it is larger than the sum of its proper divisors (10833212).

21666418 is a wasteful number, since it uses less digits than its factorization.

21666418 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10833211.

The product of its digits is 13824, while the sum is 34.

The square root of 21666418 is about 4654.7199700949. The cubic root of 21666418 is about 278.7804870567.

The spelling of 21666418 in words is "twenty-one million, six hundred sixty-six thousand, four hundred eighteen".