21781875 has 20 divisors (see below), whose sum is σ = 36294632. Its totient is φ = 11616000.

The previous prime is 21781873. The next prime is 21781891. The reversal of 21781875 is 57818712.

It is not a de Polignac number, because 21781875 - 2¹ = 21781873 is a prime.

It is a Smith number, since the sum of its digits (39) coincides with the sum of the digits of its prime factors.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21781873) 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, 3934 + ... + 7683.

Almost surely, 2^21781875 is an apocalyptic number.

21781875 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21781875 is a deficient number, since it is larger than the sum of its proper divisors (14512757).

21781875 is an equidigital number, since it uses as much as digits as its factorization.

21781875 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11640 (or 11625 counting only the distinct ones).

The product of its digits is 31360, while the sum is 39.

The square root of 21781875 is about 4667.1056341163. The cubic root of 21781875 is about 279.2748027898.

The spelling of 21781875 in words is "twenty-one million, seven hundred eighty-one thousand, eight hundred seventy-five".