21878125 has 12 divisors (see below), whose sum is σ = 27349812. Its totient is φ = 17500000.

The previous prime is 21878123. The next prime is 21878149. The reversal of 21878125 is 52187812.

It can be written as a sum of positive squares in 6 ways, for example, as 18688329 + 3189796 = 4323^2 + 1786^2 .

It is not a de Polignac number, because 21878125 - 2¹ = 21878123 is a prime.

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

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21878123) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 376 + ... + 6625.

It is an arithmetic number, because the mean of its divisors is an integer number (2279151).

Almost surely, 2^21878125 is an apocalyptic number.

21878125 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21878125 is a deficient number, since it is larger than the sum of its proper divisors (5471687).

21878125 is an frugal number, since it uses more digits than its factorization.

21878125 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7026 (or 7006 counting only the distinct ones).

The product of its digits is 8960, while the sum is 34.

The square root of 21878125 is about 4677.4057980894. The cubic root of 21878125 is about 279.6855526117.

The spelling of 21878125 in words is "twenty-one million, eight hundred seventy-eight thousand, one hundred twenty-five".