21681730 has 32 divisors (see below), whose sum is σ = 45224064. Its totient is φ = 7330176.

The previous prime is 21681721. The next prime is 21681739. The reversal of 21681730 is 3718612.

It is an interprime number because it is at equal distance from previous prime (21681721) and next prime (21681739).

It is not an unprimeable number, because it can be changed into a prime (21681739) by changing a digit.

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, 2989 + ... + 7231.

It is an arithmetic number, because the mean of its divisors is an integer number (1413252).

Almost surely, 2^21681730 is an apocalyptic number.

21681730 is an abundant number, since it is smaller than the sum of its proper divisors (23542334).

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

21681730 is a wasteful number, since it uses less digits than its factorization.

21681730 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4330.

The product of its (nonzero) digits is 2016, while the sum is 28.

The square root of 21681730 is about 4656.3644616804. The cubic root of 21681730 is about 278.8461444507.

The spelling of 21681730 in words is "twenty-one million, six hundred eighty-one thousand, seven hundred thirty".