21100666 has 4 divisors (see below), whose sum is σ = 31651002. Its totient is φ = 10550332.

The previous prime is 21100657. The next prime is 21100687. The reversal of 21100666 is 66600112.

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., 18447025 + 2653641 = 4295^2 + 1629^2 .

It is a Smith number, since the sum of its digits (22) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5275165 + ... + 5275168.

Almost surely, 2^21100666 is an apocalyptic number.

21100666 is a deficient number, since it is larger than the sum of its proper divisors (10550336).

21100666 is a wasteful number, since it uses less digits than its factorization.

21100666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10550335.

The product of its (nonzero) digits is 432, while the sum is 22.

The square root of 21100666 is about 4593.5461247276. The cubic root of 21100666 is about 276.3325561495.

Adding to 21100666 its reverse (66600112), we get a palindrome (87700778).

The spelling of 21100666 in words is "twenty-one million, one hundred thousand, six hundred sixty-six".