21581320 has 16 divisors (see below), whose sum is σ = 48558060. Its totient is φ = 8632512.

The previous prime is 21581311. The next prime is 21581327. The reversal of 21581320 is 2318512.

It can be written as a sum of positive squares in 2 ways, for example, as 20268004 + 1313316 = 4502^2 + 1146^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21581291 and 21581300.

It is not an unprimeable number, because it can be changed into a prime (21581327) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 269727 + ... + 269806.

Almost surely, 2^21581320 is an apocalyptic number.

21581320 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21581320 is an abundant number, since it is smaller than the sum of its proper divisors (26976740).

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

21581320 is a wasteful number, since it uses less digits than its factorization.

21581320 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 539544 (or 539540 counting only the distinct ones).

The product of its (nonzero) digits is 480, while the sum is 22.

The square root of 21581320 is about 4645.5699327424. The cubic root of 21581320 is about 278.4150245668.

Adding to 21581320 its reverse (2318512), we get a palindrome (23899832).

The spelling of 21581320 in words is "twenty-one million, five hundred eighty-one thousand, three hundred twenty".