21231521 has 8 divisors (see below), whose sum is σ = 22523904. Its totient is φ = 19944000.

The previous prime is 21231503. The next prime is 21231523. The reversal of 21231521 is 12513212.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 21231521 - 2¹⁴ = 21215137 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (17).

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 21231521.

It is not an unprimeable number, because it can be changed into a prime (21231523) 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, 11936 + ... + 13598.

It is an arithmetic number, because the mean of its divisors is an integer number (2815488).

Almost surely, 2^21231521 is an apocalyptic number.

It is an amenable number.

21231521 is a deficient number, since it is larger than the sum of its proper divisors (1292383).

21231521 is a wasteful number, since it uses less digits than its factorization.

21231521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2431.

The product of its digits is 120, while the sum is 17.

The square root of 21231521 is about 4607.7674637507. The cubic root of 21231521 is about 276.9026014400.

Adding to 21231521 its reverse (12513212), we get a palindrome (33744733).

The spelling of 21231521 in words is "twenty-one million, two hundred thirty-one thousand, five hundred twenty-one".