21405490 has 8 divisors (see below), whose sum is σ = 38529900. Its totient is φ = 8562192.

The previous prime is 21405473. The next prime is 21405491. The reversal of 21405490 is 9450412.

It can be written as a sum of positive squares in 2 ways, for example, as 20711601 + 693889 = 4551^2 + 833^2 .

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 (21405491) 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 3 ways as a sum of consecutive naturals, for example, 1070265 + ... + 1070284.

Almost surely, 2^21405490 is an apocalyptic number.

21405490 is a deficient number, since it is larger than the sum of its proper divisors (17124410).

21405490 is a wasteful number, since it uses less digits than its factorization.

21405490 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2140556.

The product of its (nonzero) digits is 1440, while the sum is 25.

The square root of 21405490 is about 4626.6067479309. The cubic root of 21405490 is about 277.6568493476.

The spelling of 21405490 in words is "twenty-one million, four hundred five thousand, four hundred ninety".