21280666 has 16 divisors (see below), whose sum is σ = 35481888. Its totient is φ = 9490000.

The previous prime is 21280639. The next prime is 21280687. The reversal of 21280666 is 66608212.

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 7 ways as a sum of consecutive naturals, for example, 7960 + ... + 10291.

It is an arithmetic number, because the mean of its divisors is an integer number (2217618).

Almost surely, 2^21280666 is an apocalyptic number.

21280666 is a deficient number, since it is larger than the sum of its proper divisors (14201222).

21280666 is a wasteful number, since it uses less digits than its factorization.

21280666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18317.

The product of its (nonzero) digits is 6912, while the sum is 31.

The square root of 21280666 is about 4613.0972242085. The cubic root of 21280666 is about 277.1160873536.

Adding to 21280666 its reverse (66608212), we get a palindrome (87888878).

The spelling of 21280666 in words is "twenty-one million, two hundred eighty thousand, six hundred sixty-six".