21331521 has 12 divisors (see below), whose sum is σ = 31564260. Its totient is φ = 13873920.

The previous prime is 21331487. The next prime is 21331523. The reversal of 21331521 is 12513312.

It can be written as a sum of positive squares in 2 ways, for example, as 4562496 + 16769025 = 2136^2 + 4095^2 .

It is not a de Polignac number, because 21331521 - 2¹⁰ = 21330497 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21331494 and 21331503.

It is not an unprimeable number, because it can be changed into a prime (21331523) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 28536 + ... + 29273.

It is an arithmetic number, because the mean of its divisors is an integer number (2630355).

Almost surely, 2^21331521 is an apocalyptic number.

It is an amenable number.

21331521 is a deficient number, since it is larger than the sum of its proper divisors (10232739).

21331521 is a wasteful number, since it uses less digits than its factorization.

21331521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 57856 (or 57853 counting only the distinct ones).

The product of its digits is 180, while the sum is 18.

The square root of 21331521 is about 4618.6059585117. The cubic root of 21331521 is about 277.3366557569.

Adding to 21331521 its reverse (12513312), we get a palindrome (33844833).

The spelling of 21331521 in words is "twenty-one million, three hundred thirty-one thousand, five hundred twenty-one".