21172385 has 8 divisors (see below), whose sum is σ = 27361320. Its totient is φ = 15634944.

The previous prime is 21172381. The next prime is 21172423. The reversal of 21172385 is 58327112.

It can be written as a sum of positive squares in 4 ways, for example, as 1423249 + 19749136 = 1193^2 + 4444^2 .

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

It is not a de Polignac number, because 21172385 - 2² = 21172381 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21172381) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 162800 + ... + 162929.

It is an arithmetic number, because the mean of its divisors is an integer number (3420165).

Almost surely, 2^21172385 is an apocalyptic number.

It is an amenable number.

21172385 is a deficient number, since it is larger than the sum of its proper divisors (6188935).

21172385 is a wasteful number, since it uses less digits than its factorization.

21172385 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 325747.

The product of its digits is 3360, while the sum is 29.

The square root of 21172385 is about 4601.3459987269. The cubic root of 21172385 is about 276.6452774548.

Adding to 21172385 its reverse (58327112), we get a palindrome (79499497).

The spelling of 21172385 in words is "twenty-one million, one hundred seventy-two thousand, three hundred eighty-five".