21185707 has 4 divisors (see below), whose sum is σ = 21209680. Its totient is φ = 21161736.

The previous prime is 21185693. The next prime is 21185729. The reversal of 21185707 is 70758112.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21185707 - 2¹⁹ = 20661419 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21185777) 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 3 ways as a sum of consecutive naturals, for example, 10608 + ... + 12445.

It is an arithmetic number, because the mean of its divisors is an integer number (5302420).

Almost surely, 2^21185707 is an apocalyptic number.

21185707 is a deficient number, since it is larger than the sum of its proper divisors (23973).

21185707 is an equidigital number, since it uses as much as digits as its factorization.

21185707 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23972.

The product of its (nonzero) digits is 3920, while the sum is 31.

The square root of 21185707 is about 4602.7933909747. The cubic root of 21185707 is about 276.7032884862.

The spelling of 21185707 in words is "twenty-one million, one hundred eighty-five thousand, seven hundred seven".