21978125 has 24 divisors (see below), whose sum is σ = 29638728. Its totient is φ = 16200000.

The previous prime is 21978109. The next prime is 21978137. The reversal of 21978125 is 52187912.

It can be written as a sum of positive squares in 12 ways, for example, as 21031396 + 946729 = 4586^2 + 973^2 .

It is not a de Polignac number, because 21978125 - 2⁴ = 21978109 is a prime.

It is a Duffinian number.

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 23 ways as a sum of consecutive naturals, for example, 40355 + ... + 40895.

It is an arithmetic number, because the mean of its divisors is an integer number (1234947).

Almost surely, 2^21978125 is an apocalyptic number.

21978125 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21978125 is a deficient number, since it is larger than the sum of its proper divisors (7660603).

21978125 is an frugal number, since it uses more digits than its factorization.

21978125 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 579 (or 559 counting only the distinct ones).

The product of its digits is 10080, while the sum is 35.

The square root of 21978125 is about 4688.0832970416. The cubic root of 21978125 is about 280.1110316458. Note that the first 3 decimals are identical.

It can be divided in two parts, 2197 and 8125, that multiplied together give a 4-th power (17850625 = 65⁴).

The spelling of 21978125 in words is "twenty-one million, nine hundred seventy-eight thousand, one hundred twenty-five".