21658666 has 4 divisors (see below), whose sum is σ = 32488002. Its totient is φ = 10829332.

The previous prime is 21658657. The next prime is 21658669. The reversal of 21658666 is 66685612.

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., 11868025 + 9790641 = 3445^2 + 3129^2 .

It is not an unprimeable number, because it can be changed into a prime (21658669) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5414665 + ... + 5414668.

Almost surely, 2^21658666 is an apocalyptic number.

21658666 is a deficient number, since it is larger than the sum of its proper divisors (10829336).

21658666 is a wasteful number, since it uses less digits than its factorization.

21658666 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10829335.

The product of its digits is 103680, while the sum is 40.

The square root of 21658666 is about 4653.8871924446. The cubic root of 21658666 is about 278.7472349193.

The spelling of 21658666 in words is "twenty-one million, six hundred fifty-eight thousand, six hundred sixty-six".