21125715 has 32 divisors (see below), whose sum is σ = 36723456. Its totient is φ = 10308480.

The previous prime is 21125711. The next prime is 21125723. The reversal of 21125715 is 51752112.

It is not a de Polignac number, because 21125715 - 2² = 21125711 is a prime.

It is a super-2 number, since 2×21125715² = 892591668522450, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21125711) by changing a digit.

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 31 ways as a sum of consecutive naturals, for example, 25132 + ... + 25958.

It is an arithmetic number, because the mean of its divisors is an integer number (1147608).

Almost surely, 2^21125715 is an apocalyptic number.

21125715 is a deficient number, since it is larger than the sum of its proper divisors (15597741).

21125715 is a wasteful number, since it uses less digits than its factorization.

21125715 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 979.

The product of its digits is 700, while the sum is 24.

The square root of 21125715 is about 4596.2718588003. The cubic root of 21125715 is about 276.4418594448.

Adding to 21125715 its reverse (51752112), we get a palindrome (72877827).

The spelling of 21125715 in words is "twenty-one million, one hundred twenty-five thousand, seven hundred fifteen".