21991925 has 12 divisors (see below), whose sum is σ = 27473316. Its totient is φ = 17462400.

The previous prime is 21991919. The next prime is 21991939. The reversal of 21991925 is 52919912.

It can be written as a sum of positive squares in 6 ways, for example, as 988036 + 21003889 = 994^2 + 4583^2 .

It is not a de Polignac number, because 21991925 - 2⁴ = 21991909 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 215 + ... + 6635.

It is an arithmetic number, because the mean of its divisors is an integer number (2289443).

Almost surely, 2^21991925 is an apocalyptic number.

21991925 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21991925 is a deficient number, since it is larger than the sum of its proper divisors (5481391).

21991925 is a wasteful number, since it uses less digits than its factorization.

21991925 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6568 (or 6563 counting only the distinct ones).

The product of its digits is 14580, while the sum is 38.

The square root of 21991925 is about 4689.5548829287. The cubic root of 21991925 is about 280.1696463436.

The spelling of 21991925 in words is "twenty-one million, nine hundred ninety-one thousand, nine hundred twenty-five".