21681725 has 12 divisors (see below), whose sum is σ = 28953876. Its totient is φ = 16010880.

The previous prime is 21681721. The next prime is 21681739. The reversal of 21681725 is 52718612.

It can be written as a sum of positive squares in 6 ways, for example, as 466489 + 21215236 = 683^2 + 4606^2 .

It is not a de Polignac number, because 21681725 - 2² = 21681721 is a prime.

It is a hoax number, since the sum of its digits (32) coincides with the sum of the digits of its distinct prime factors.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21681691 and 21681700.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21681721) 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, 33032 + ... + 33681.

It is an arithmetic number, because the mean of its divisors is an integer number (2412823).

Almost surely, 2^21681725 is an apocalyptic number.

21681725 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21681725 is a deficient number, since it is larger than the sum of its proper divisors (7272151).

21681725 is a wasteful number, since it uses less digits than its factorization.

21681725 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 66736 (or 66731 counting only the distinct ones).

The product of its digits is 6720, while the sum is 32.

The square root of 21681725 is about 4656.3639247808. The cubic root of 21681725 is about 278.8461230159.

The spelling of 21681725 in words is "twenty-one million, six hundred eighty-one thousand, seven hundred twenty-five".