21125731 has 4 divisors (see below), whose sum is σ = 23046264. Its totient is φ = 19205200.

The previous prime is 21125729. The next prime is 21125737. The reversal of 21125731 is 13752112.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21125731 - 2¹ = 21125729 is a prime.

It is a super-2 number, since 2×21125731² = 892593020568722, which contains 22 as substring.

It is a Smith number, since the sum of its digits (22) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21125737) 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 3 ways as a sum of consecutive naturals, for example, 960250 + ... + 960271.

It is an arithmetic number, because the mean of its divisors is an integer number (5761566).

Almost surely, 2^21125731 is an apocalyptic number.

21125731 is a deficient number, since it is larger than the sum of its proper divisors (1920533).

21125731 is a wasteful number, since it uses less digits than its factorization.

21125731 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1920532.

The product of its digits is 420, while the sum is 22.

The square root of 21125731 is about 4596.2735993411. The cubic root of 21125731 is about 276.4419292345.

Adding to 21125731 its reverse (13752112), we get a palindrome (34877843).

The spelling of 21125731 in words is "twenty-one million, one hundred twenty-five thousand, seven hundred thirty-one".