21405730 has 8 divisors (see below), whose sum is σ = 38530332. Its totient is φ = 8562288.

The previous prime is 21405691. The next prime is 21405733. The reversal of 21405730 is 3750412.

It can be written as a sum of positive squares in 2 ways, for example, as 20439441 + 966289 = 4521^2 + 983^2 .

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

It is not an unprimeable number, because it can be changed into a prime (21405733) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1070277 + ... + 1070296.

Almost surely, 2^21405730 is an apocalyptic number.

21405730 is a deficient number, since it is larger than the sum of its proper divisors (17124602).

21405730 is a wasteful number, since it uses less digits than its factorization.

21405730 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2140580.

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

The square root of 21405730 is about 4626.6326847936. The cubic root of 21405730 is about 277.6578870470.

The spelling of 21405730 in words is "twenty-one million, four hundred five thousand, seven hundred thirty".