21387173 has 8 divisors (see below), whose sum is σ = 22702680. Its totient is φ = 20078080.

The previous prime is 21387167. The next prime is 21387193. The reversal of 21387173 is 37178312.

It can be written as a sum of positive squares in 4 ways, for example, as 9840769 + 11546404 = 3137^2 + 3398^2 .

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

It is a cyclic number.

It is not a de Polignac number, because 21387173 - 2⁶ = 21387109 is a prime.

It is a super-2 number, since 2×21387173² = 914822337863858, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21387193) by changing a digit.

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, 6473 + ... + 9201.

It is an arithmetic number, because the mean of its divisors is an integer number (2837835).

Almost surely, 2^21387173 is an apocalyptic number.

It is an amenable number.

21387173 is a deficient number, since it is larger than the sum of its proper divisors (1315507).

21387173 is a wasteful number, since it uses less digits than its factorization.

21387173 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3207.

The product of its digits is 7056, while the sum is 32.

The square root of 21387173 is about 4624.6267957534. The cubic root of 21387173 is about 277.5776283646.

The spelling of 21387173 in words is "twenty-one million, three hundred eighty-seven thousand, one hundred seventy-three".