21909744 has 80 divisors (see below), whose sum is σ = 64475040. Its totient is φ = 7119360.

The previous prime is 21909743. The next prime is 21909799. The reversal of 21909744 is 44790912.

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 = 21909699 and 21909708.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21909743) 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 15 ways as a sum of consecutive naturals, for example, 17094 + ... + 18330.

It is an arithmetic number, because the mean of its divisors is an integer number (805938).

Almost surely, 2^21909744 is an apocalyptic number.

21909744 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 21909744, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32237520).

21909744 is an abundant number, since it is smaller than the sum of its proper divisors (42565296).

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

21909744 is a wasteful number, since it uses less digits than its factorization.

21909744 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1295 (or 1283 counting only the distinct ones).

The product of its (nonzero) digits is 18144, while the sum is 36.

The square root of 21909744 is about 4680.7845496241. The cubic root of 21909744 is about 279.8202247352.

The spelling of 21909744 in words is "twenty-one million, nine hundred nine thousand, seven hundred forty-four".