21009406 has 8 divisors (see below), whose sum is σ = 34379064. Its totient is φ = 9549720.

The previous prime is 21009403. The next prime is 21009407. The reversal of 21009406 is 60490012.

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

It is a Harshad number since it is a multiple of its sum of digits (22), and also a Moran number because the ratio is a prime number: 954973 = 21009406 / (2 + 1 + 0 + 0 + 9 + 4 + 0 + 6).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21009403) 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, 477465 + ... + 477508.

It is an arithmetic number, because the mean of its divisors is an integer number (4297383).

Almost surely, 2^21009406 is an apocalyptic number.

21009406 is a deficient number, since it is larger than the sum of its proper divisors (13369658).

21009406 is a wasteful number, since it uses less digits than its factorization.

21009406 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 954986.

The product of its (nonzero) digits is 432, while the sum is 22.

The square root of 21009406 is about 4583.6018588006. The cubic root of 21009406 is about 275.9336026656.

Adding to 21009406 its reverse (60490012), we get a palindrome (81499418).

The spelling of 21009406 in words is "twenty-one million, nine thousand, four hundred six".