21730518 has 48 divisors (see below), whose sum is σ = 49694736. Its totient is φ = 7115040.

The previous prime is 21730517. The next prime is 21730519. The reversal of 21730518 is 81503712.

It is an interprime number because it is at equal distance from previous prime (21730517) and next prime (21730519).

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a junction number, because it is equal to n+sod(n) for n = 21730491 and 21730500.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21730517) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 29280 + ... + 30012.

It is an arithmetic number, because the mean of its divisors is an integer number (1035307).

Almost surely, 2^21730518 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21730518, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24847368).

21730518 is an abundant number, since it is smaller than the sum of its proper divisors (27964218).

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

21730518 is an equidigital number, since it uses as much as digits as its factorization.

21730518 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 811 (or 799 counting only the distinct ones).

The product of its (nonzero) digits is 1680, while the sum is 27.

The square root of 21730518 is about 4661.6003689720. The cubic root of 21730518 is about 279.0551399862.

The spelling of 21730518 in words is "twenty-one million, seven hundred thirty thousand, five hundred eighteen".