21817320 has 128 divisors (see below), whose sum is σ = 78796800. Its totient is φ = 4720896.

The previous prime is 21817261. The next prime is 21817333. The reversal of 21817320 is 2371812.

It is a super-3 number, since 3×21817320³ (a number of 23 digits) contains 333 as substring.

It is a Harshad number since it is a multiple of its sum of digits (24).

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 15277 + ... + 16643.

It is an arithmetic number, because the mean of its divisors is an integer number (615600).

Almost surely, 2^21817320 is an apocalyptic number.

21817320 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 21817320, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (39398400).

21817320 is an abundant number, since it is smaller than the sum of its proper divisors (56979480).

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

21817320 is a wasteful number, since it uses less digits than its factorization.

21817320 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1407 (or 1403 counting only the distinct ones).

The product of its (nonzero) digits is 672, while the sum is 24.

The square root of 21817320 is about 4670.9014119332. The cubic root of 21817320 is about 279.4262058996.

The spelling of 21817320 in words is "twenty-one million, eight hundred seventeen thousand, three hundred twenty".