21156668 has 12 divisors (see below), whose sum is σ = 39872280. Its totient is φ = 9764592.

The previous prime is 21156661. The next prime is 21156701. The reversal of 21156668 is 86665112.

It is a happy number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21156661) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 203378 + ... + 203481.

It is an arithmetic number, because the mean of its divisors is an integer number (3322690).

Almost surely, 2^21156668 is an apocalyptic number.

It is an amenable number.

21156668 is a deficient number, since it is larger than the sum of its proper divisors (18715612).

21156668 is a wasteful number, since it uses less digits than its factorization.

21156668 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 406876 (or 406874 counting only the distinct ones).

The product of its digits is 17280, while the sum is 35.

The square root of 21156668 is about 4599.6378118282. The cubic root of 21156668 is about 276.5768060290.

The spelling of 21156668 in words is "twenty-one million, one hundred fifty-six thousand, six hundred sixty-eight".