21638125 has 20 divisors (see below), whose sum is σ = 27413100. Its totient is φ = 17072000.

The previous prime is 21638117. The next prime is 21638129. The reversal of 21638125 is 52183612.

It can be written as a sum of positive squares in 10 ways, for example, as 20811844 + 826281 = 4562^2 + 909^2 .

It is not a de Polignac number, because 21638125 - 2³ = 21638117 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a junction number, because it is equal to n+sod(n) for n = 21638093 and 21638102.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21638129) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 55431 + ... + 55819.

It is an arithmetic number, because the mean of its divisors is an integer number (1370655).

Almost surely, 2^21638125 is an apocalyptic number.

21638125 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21638125 is a deficient number, since it is larger than the sum of its proper divisors (5774975).

21638125 is an frugal number, since it uses more digits than its factorization.

21638125 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 498 (or 483 counting only the distinct ones).

The product of its digits is 2880, while the sum is 28.

The square root of 21638125 is about 4651.6798041138. The cubic root of 21638125 is about 278.6590860924.

The spelling of 21638125 in words is "twenty-one million, six hundred thirty-eight thousand, one hundred twenty-five".