21125531 has 8 divisors (see below), whose sum is σ = 24259584. Its totient is φ = 18020520.

The previous prime is 21125521. The next prime is 21125551. The reversal of 21125531 is 13552112.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a de Polignac number, because none of the positive numbers 2^k-21125531 is a prime.

It is a super-2 number, since 2×21125531² = 892576120063922, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21125501) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 5675 + ... + 8628.

It is an arithmetic number, because the mean of its divisors is an integer number (3032448).

Almost surely, 2^21125531 is an apocalyptic number.

21125531 is a deficient number, since it is larger than the sum of its proper divisors (3134053).

21125531 is a wasteful number, since it uses less digits than its factorization.

21125531 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14521.

The product of its digits is 300, while the sum is 20.

The square root of 21125531 is about 4596.2518425343. The cubic root of 21125531 is about 276.4410568613.

Adding to 21125531 its reverse (13552112), we get a palindrome (34677643).

It can be divided in two parts, 211 and 25531, that multiplied together give a square (5387041 = 2321²).

The spelling of 21125531 in words is "twenty-one million, one hundred twenty-five thousand, five hundred thirty-one".