21209766 has 16 divisors (see below), whose sum is σ = 43788288. Its totient is φ = 6841800.

The previous prime is 21209743. The next prime is 21209779. The reversal of 21209766 is 66790212.

It is a congruent number.

It is an unprimeable number.

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 in 7 ways as a sum of consecutive naturals, for example, 56830 + ... + 57201.

It is an arithmetic number, because the mean of its divisors is an integer number (2736768).

Almost surely, 2^21209766 is an apocalyptic number.

21209766 is an abundant number, since it is smaller than the sum of its proper divisors (22578522).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21209766 is a wasteful number, since it uses less digits than its factorization.

21209766 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 114067.

The product of its (nonzero) digits is 9072, while the sum is 33.

The square root of 21209766 is about 4605.4061710125. The cubic root of 21209766 is about 276.8079925048.

Adding to 21209766 its reverse (66790212), we get a palindrome (87999978).

The spelling of 21209766 in words is "twenty-one million, two hundred nine thousand, seven hundred sixty-six".