21521320 has 32 divisors (see below), whose sum is σ = 51273000. Its totient is φ = 8101888.

The previous prime is 21521317. The next prime is 21521321. The reversal of 21521320 is 2312512.

It can be written as a sum of positive squares in 4 ways, for example, as 21288996 + 232324 = 4614^2 + 482^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21521294 and 21521303.

It is not an unprimeable number, because it can be changed into a prime (21521321) 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, 15145 + ... + 16504.

Almost surely, 2^21521320 is an apocalyptic number.

21521320 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21521320 is an abundant number, since it is smaller than the sum of its proper divisors (29751680).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21521320 is a wasteful number, since it uses less digits than its factorization.

21521320 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 31677 (or 31673 counting only the distinct ones).

The product of its (nonzero) digits is 120, while the sum is 16.

The square root of 21521320 is about 4639.1076728181. The cubic root of 21521320 is about 278.1567702629.

Adding to 21521320 its reverse (2312512), we get a palindrome (23833832).

The spelling of 21521320 in words is "twenty-one million, five hundred twenty-one thousand, three hundred twenty".