21745724 has 48 divisors (see below), whose sum is σ = 51104256. Its totient is φ = 7819200.

The previous prime is 21745697. The next prime is 21745727. The reversal of 21745724 is 42754712.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21745727) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1289 + ... + 6719.

It is an arithmetic number, because the mean of its divisors is an integer number (1064672).

Almost surely, 2^21745724 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21745724, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25552128).

21745724 is an abundant number, since it is smaller than the sum of its proper divisors (29358532).

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

21745724 is a wasteful number, since it uses less digits than its factorization.

21745724 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5466 (or 5464 counting only the distinct ones).

The product of its digits is 15680, while the sum is 32.

The square root of 21745724 is about 4663.2310686905. The cubic root of 21745724 is about 279.1202147210.

The spelling of 21745724 in words is "twenty-one million, seven hundred forty-five thousand, seven hundred twenty-four".