21510725 has 12 divisors (see below), whose sum is σ = 27242304. Its totient is φ = 16841520.

The previous prime is 21510719. The next prime is 21510733. The reversal of 21510725 is 52701512.

It is a happy number.

It is not a de Polignac number, because 21510725 - 2⁸ = 21510469 is a prime.

It is a super-2 number, since 2×21510725² = 925422580051250, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21510725.

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, 7979 + ... + 10328.

It is an arithmetic number, because the mean of its divisors is an integer number (2270192).

Almost surely, 2^21510725 is an apocalyptic number.

21510725 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21510725 is a deficient number, since it is larger than the sum of its proper divisors (5731579).

21510725 is a wasteful number, since it uses less digits than its factorization.

21510725 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18364 (or 18359 counting only the distinct ones).

The product of its (nonzero) digits is 700, while the sum is 23.

The square root of 21510725 is about 4637.9656100493. The cubic root of 21510725 is about 278.1111170110. Note that the first 5 decimals are identical.

The spelling of 21510725 in words is "twenty-one million, five hundred ten thousand, seven hundred twenty-five".