21186921 has 8 divisors (see below), whose sum is σ = 32284864. Its totient is φ = 12106800.

The previous prime is 21186911. The next prime is 21186929. The reversal of 21186921 is 12968112.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21186921 - 2⁷ = 21186793 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21186929) 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 in 7 ways as a sum of consecutive naturals, for example, 504430 + ... + 504471.

It is an arithmetic number, because the mean of its divisors is an integer number (4035608).

Almost surely, 2^21186921 is an apocalyptic number.

21186921 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21186921 is a deficient number, since it is larger than the sum of its proper divisors (11097943).

21186921 is a wasteful number, since it uses less digits than its factorization.

21186921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1008911.

The product of its digits is 1728, while the sum is 30.

The square root of 21186921 is about 4602.9252655241. The cubic root of 21186921 is about 276.7085736749.

The spelling of 21186921 in words is "twenty-one million, one hundred eighty-six thousand, nine hundred twenty-one".