21691925 has 6 divisors (see below), whose sum is σ = 26898018. Its totient is φ = 17353520.

The previous prime is 21691919. The next prime is 21691927. The reversal of 21691925 is 52919612.

It can be written as a sum of positive squares in 3 ways, for example, as 5635876 + 16056049 = 2374^2 + 4007^2 .

It is not a de Polignac number, because 21691925 - 2²² = 17497621 is a prime.

It is a super-2 number, since 2×21691925² = 941079220411250, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21691927) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 433814 + ... + 433863.

It is an arithmetic number, because the mean of its divisors is an integer number (4483003).

Almost surely, 2^21691925 is an apocalyptic number.

21691925 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21691925 is a deficient number, since it is larger than the sum of its proper divisors (5206093).

21691925 is an equidigital number, since it uses as much as digits as its factorization.

21691925 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 867687 (or 867682 counting only the distinct ones).

The product of its digits is 9720, while the sum is 35.

The square root of 21691925 is about 4657.4590712104. The cubic root of 21691925 is about 278.8898431621.

The spelling of 21691925 in words is "twenty-one million, six hundred ninety-one thousand, nine hundred twenty-five".