20721280 has 32 divisors (see below), whose sum is σ = 49538340. Its totient is φ = 8288256.

The previous prime is 20721271. The next prime is 20721287. The reversal of 20721280 is 8212702.

It can be written as a sum of positive squares in 2 ways, for example, as 20720704 + 576 = 4552^2 + 24^2 .

It is a tau number, because it is divible by the number of its divisors (32).

It is not an unprimeable number, because it can be changed into a prime (20721287) 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, 15549 + ... + 16828.

Almost surely, 2^20721280 is an apocalyptic number.

20721280 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

20721280 is an abundant number, since it is smaller than the sum of its proper divisors (28817060).

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

20721280 is an equidigital number, since it uses as much as digits as its factorization.

20721280 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 32396 (or 32384 counting only the distinct ones).

The product of its (nonzero) digits is 448, while the sum is 22.

The square root of 20721280 is about 4552.0632684531. The cubic root of 20721280 is about 274.6663943609. Note that the first 3 decimals are identical.

Adding to 20721280 its reverse (8212702), we get a palindrome (28933982).

The spelling of 20721280 in words is "twenty million, seven hundred twenty-one thousand, two hundred eighty".