21691666 has 8 divisors (see below), whose sum is σ = 32681520. Its totient is φ = 10797828.

The previous prime is 21691633. The next prime is 21691693. The reversal of 21691666 is 66619612.

It is a sphenic number, since it is the product of 3 distinct primes.

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 in 3 ways as a sum of consecutive naturals, for example, 23436 + ... + 24343.

It is an arithmetic number, because the mean of its divisors is an integer number (4085190).

Almost surely, 2^21691666 is an apocalyptic number.

21691666 is a deficient number, since it is larger than the sum of its proper divisors (10989854).

21691666 is a wasteful number, since it uses less digits than its factorization.

21691666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 48008.

The product of its digits is 23328, while the sum is 37.

The square root of 21691666 is about 4657.4312662668. The cubic root of 21691666 is about 278.8887331829. Note that the first 3 decimals are identical.

The spelling of 21691666 in words is "twenty-one million, six hundred ninety-one thousand, six hundred sixty-six".