21721730 has 8 divisors (see below), whose sum is σ = 39099132. Its totient is φ = 8688688.

The previous prime is 21721727. The next prime is 21721741. The reversal of 21721730 is 3712712.

It can be written as a sum of positive squares in 2 ways, for example, as 21501769 + 219961 = 4637^2 + 469^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a junction number, because it is equal to n+sod(n) for n = 21721696 and 21721705.

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 3 ways as a sum of consecutive naturals, for example, 1086077 + ... + 1086096.

Almost surely, 2^21721730 is an apocalyptic number.

21721730 is a deficient number, since it is larger than the sum of its proper divisors (17377402).

21721730 is a wasteful number, since it uses less digits than its factorization.

21721730 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2172180.

The product of its (nonzero) digits is 588, while the sum is 23.

The square root of 21721730 is about 4660.6576789119. The cubic root of 21721730 is about 279.0175175171.

The spelling of 21721730 in words is "twenty-one million, seven hundred twenty-one thousand, seven hundred thirty".