21605025 has 24 divisors (see below), whose sum is σ = 38469760. Its totient is φ = 10635840.

The previous prime is 21605009. The next prime is 21605039. The reversal of 21605025 is 52050612.

It is not a de Polignac number, because 21605025 - 2⁴ = 21605009 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21604992 and 21605010.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 10105 + ... + 12054.

Almost surely, 2^21605025 is an apocalyptic number.

21605025 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21605025 is a deficient number, since it is larger than the sum of its proper divisors (16864735).

21605025 is a wasteful number, since it uses less digits than its factorization.

21605025 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 22185 (or 22180 counting only the distinct ones).

The product of its (nonzero) digits is 600, while the sum is 21.

The square root of 21605025 is about 4648.1205879366. The cubic root of 21605025 is about 278.5169246237.

Adding to 21605025 its reverse (52050612), we get a palindrome (73655637).

The spelling of 21605025 in words is "twenty-one million, six hundred five thousand, twenty-five".