21390685 has 8 divisors (see below), whose sum is σ = 25694136. Its totient is φ = 17095680.

The previous prime is 21390673. The next prime is 21390727. The reversal of 21390685 is 58609312.

It can be written as a sum of positive squares in 4 ways, for example, as 1194649 + 20196036 = 1093^2 + 4494^2 .

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

It is not a de Polignac number, because 21390685 - 2⁷ = 21390557 is a prime.

It is a super-2 number, since 2×21390685² = 915122809538450, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21390685.

It is a congruent number.

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, 7225 + ... + 9745.

It is an arithmetic number, because the mean of its divisors is an integer number (3211767).

Almost surely, 2^21390685 is an apocalyptic number.

It is an amenable number.

21390685 is a deficient number, since it is larger than the sum of its proper divisors (4303451).

21390685 is a wasteful number, since it uses less digits than its factorization.

21390685 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4223.

The product of its (nonzero) digits is 12960, while the sum is 34.

The square root of 21390685 is about 4625.0064864819. The cubic root of 21390685 is about 277.5928212604.

Adding to 21390685 its reverse (58609312), we get a palindrome (79999997).

The spelling of 21390685 in words is "twenty-one million, three hundred ninety thousand, six hundred eighty-five".