21279744 has 66 divisors (see below), whose sum is σ = 61471410. Its totient is φ = 7090176.

The previous prime is 21279737. The next prime is 21279749. The reversal of 21279744 is 44797212.

It can be written as a sum of positive squares in only one way, i.e., 20358144 + 921600 = 4512^2 + 960^2 .

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a junction number, because it is equal to n+sod(n) for n = 21279699 and 21279708.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21279749) 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 5 ways as a sum of consecutive naturals, for example, 8062 + ... + 10370.

It is an arithmetic number, because the mean of its divisors is an integer number (931385).

Almost surely, 2^21279744 is an apocalyptic number.

21279744 is a gapful number since it is divisible by the number (24) 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 21279744, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30735705).

21279744 is an abundant number, since it is smaller than the sum of its proper divisors (40191666).

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

21279744 is a wasteful number, since it uses less digits than its factorization.

21279744 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2335 (or 2314 counting only the distinct ones).

The product of its digits is 28224, while the sum is 36.

The square root of 21279744 is about 4612.9972902658. The cubic root of 21279744 is about 277.1120852119.

The spelling of 21279744 in words is "twenty-one million, two hundred seventy-nine thousand, seven hundred forty-four".