21729280 has 52 divisors (see below), whose sum is σ = 52193052. Its totient is φ = 8683520.

The previous prime is 21729269. The next prime is 21729289. The reversal of 21729280 is 8292712.

It can be written as a sum of positive squares in 2 ways, for example, as 11075584 + 10653696 = 3328^2 + 3264^2 .

It is not an unprimeable number, because it can be changed into a prime (21729289) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 19950 + ... + 21010.

Almost surely, 2^21729280 is an apocalyptic number.

21729280 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21729280, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26096526).

21729280 is an abundant number, since it is smaller than the sum of its proper divisors (30463772).

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

21729280 is an equidigital number, since it uses as much as digits as its factorization.

21729280 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1090 (or 1068 counting only the distinct ones).

The product of its (nonzero) digits is 4032, while the sum is 31.

The square root of 21729280 is about 4661.4675800653. The cubic root of 21729280 is about 279.0498405754.

The spelling of 21729280 in words is "twenty-one million, seven hundred twenty-nine thousand, two hundred eighty".