21723840 has 168 divisors, whose sum is σ = 78851760. Its totient is φ = 5474304.

The previous prime is 21723797. The next prime is 21723853. The reversal of 21723840 is 4832712.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 54522 + ... + 54918.

Almost surely, 2^21723840 is an apocalyptic number.

21723840 is a gapful number since it is divisible by the number (20) 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 21723840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (39425880).

21723840 is an abundant number, since it is smaller than the sum of its proper divisors (57127920).

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

21723840 is a wasteful number, since it uses less digits than its factorization.

21723840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 439 (or 426 counting only the distinct ones).

The product of its (nonzero) digits is 2688, while the sum is 27.

The square root of 21723840 is about 4660.8840363176. The cubic root of 21723840 is about 279.0265516027.

The spelling of 21723840 in words is "twenty-one million, seven hundred twenty-three thousand, eight hundred forty".