21555025 has 24 divisors (see below), whose sum is σ = 29373120. Its totient is φ = 15618240.

The previous prime is 21555007. The next prime is 21555029. The reversal of 21555025 is 52055512.

It is a happy number.

It is not a de Polignac number, because 21555025 - 2⁵ = 21554993 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (25).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21555029) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 9939 + ... + 11911.

It is an arithmetic number, because the mean of its divisors is an integer number (1223880).

Almost surely, 2^21555025 is an apocalyptic number.

21555025 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21555025 is a deficient number, since it is larger than the sum of its proper divisors (7818095).

21555025 is a wasteful number, since it uses less digits than its factorization.

21555025 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2025 (or 2020 counting only the distinct ones).

The product of its (nonzero) digits is 2500, while the sum is 25.

The square root of 21555025 is about 4642.7389545397. The cubic root of 21555025 is about 278.3019036148.

The spelling of 21555025 in words is "twenty-one million, five hundred fifty-five thousand, twenty-five".