21131866 has 16 divisors (see below), whose sum is σ = 36285120. Its totient is φ = 9041760.

The previous prime is 21131827. The next prime is 21131881. The reversal of 21131866 is 66813112.

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, 15750 + ... + 17038.

It is an arithmetic number, because the mean of its divisors is an integer number (2267820).

Almost surely, 2^21131866 is an apocalyptic number.

21131866 is a deficient number, since it is larger than the sum of its proper divisors (15153254).

21131866 is a wasteful number, since it uses less digits than its factorization.

21131866 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2469.

The product of its digits is 1728, while the sum is 28.

The square root of 21131866 is about 4596.9409393639. The cubic root of 21131866 is about 276.4686866058.

Adding to 21131866 its reverse (66813112), we get a palindrome (87944978).

The spelling of 21131866 in words is "twenty-one million, one hundred thirty-one thousand, eight hundred sixty-six".