21657866 has 4 divisors (see below), whose sum is σ = 32486802. Its totient is φ = 10828932.

The previous prime is 21657863. The next prime is 21657877. The reversal of 21657866 is 66875612.

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., 13845841 + 7812025 = 3721^2 + 2795^2 .

It is not an unprimeable number, because it can be changed into a prime (21657863) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5414465 + ... + 5414468.

Almost surely, 2^21657866 is an apocalyptic number.

21657866 is a deficient number, since it is larger than the sum of its proper divisors (10828936).

21657866 is a wasteful number, since it uses less digits than its factorization.

21657866 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10828935.

The product of its digits is 120960, while the sum is 41.

The square root of 21657866 is about 4653.8012419956. The cubic root of 21657866 is about 278.7438028746.

The spelling of 21657866 in words is "twenty-one million, six hundred fifty-seven thousand, eight hundred sixty-six".