21639744 has 112 divisors (see below), whose sum is σ = 72745600. Its totient is φ = 6179328.

The previous prime is 21639731. The next prime is 21639769. The reversal of 21639744 is 44793612.

It is a tau number, because it is divible by the number of its divisors (112).

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

It is a nude number because it is divisible by every one of its digits.

It is a junction number, because it is equal to n+sod(n) for n = 21639699 and 21639708.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 11202 + ... + 12990.

Almost surely, 2^21639744 is an apocalyptic number.

21639744 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 21639744, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36372800).

21639744 is an abundant number, since it is smaller than the sum of its proper divisors (51105856).

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

21639744 is a wasteful number, since it uses less digits than its factorization.

21639744 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1817 (or 1801 counting only the distinct ones).

The product of its digits is 36288, while the sum is 36.

The square root of 21639744 is about 4651.8538240147. The cubic root of 21639744 is about 278.6660358290. Note that the first 3 decimals are identical.

The spelling of 21639744 in words is "twenty-one million, six hundred thirty-nine thousand, seven hundred forty-four".