21723520 has 128 divisors (see below), whose sum is σ = 64088640. Its totient is φ = 6856704.

The previous prime is 21723469. The next prime is 21723539. The reversal of 21723520 is 2532712.

It is a tau number, because it is divible by the number of its divisors (128).

It is a super-2 number, since 2×21723520² = 943822642380800, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21723491 and 21723500.

It is a congruent number.

It is an unprimeable number.

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, 58054 + ... + 58426.

Almost surely, 2^21723520 is an apocalyptic number.

21723520 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 21723520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32044320).

21723520 is an abundant number, since it is smaller than the sum of its proper divisors (42365120).

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

21723520 is a wasteful number, since it uses less digits than its factorization.

21723520 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 412 (or 400 counting only the distinct ones).

The product of its (nonzero) digits is 840, while the sum is 22.

The square root of 21723520 is about 4660.8497079395. The cubic root of 21723520 is about 279.0251815420.

The spelling of 21723520 in words is "twenty-one million, seven hundred twenty-three thousand, five hundred twenty".