21309288 has 128 divisors (see below), whose sum is σ = 71608320. Its totient is φ = 5103360.

The previous prime is 21309263. The next prime is 21309289. The reversal of 21309288 is 88290312.

It is a Harshad number since it is a multiple of its sum of digits (33).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21309289) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 23581 + ... + 24467.

It is an arithmetic number, because the mean of its divisors is an integer number (559440).

Almost surely, 2^21309288 is an apocalyptic number.

21309288 is a gapful number since it is divisible by the number (28) 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 21309288, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (35804160).

21309288 is an abundant number, since it is smaller than the sum of its proper divisors (50299032).

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

21309288 is a wasteful number, since it uses less digits than its factorization.

21309288 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 927 (or 923 counting only the distinct ones).

The product of its (nonzero) digits is 6912, while the sum is 33.

The square root of 21309288 is about 4616.1984359427. The cubic root of 21309288 is about 277.2402699232.

The spelling of 21309288 in words is "twenty-one million, three hundred nine thousand, two hundred eighty-eight".