21006905 has 8 divisors (see below), whose sum is σ = 25315200. Its totient is φ = 16734256.

The previous prime is 21006899. The next prime is 21006907. The reversal of 21006905 is 50960012.

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

It is a cyclic number.

It is not a de Polignac number, because 21006905 - 2¹⁴ = 20990521 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21006907) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 7595 + ... + 9984.

It is an arithmetic number, because the mean of its divisors is an integer number (3164400).

Almost surely, 2^21006905 is an apocalyptic number.

It is an amenable number.

21006905 is a deficient number, since it is larger than the sum of its proper divisors (4308295).

21006905 is a wasteful number, since it uses less digits than its factorization.

21006905 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17823.

The product of its (nonzero) digits is 540, while the sum is 23.

The square root of 21006905 is about 4583.3290303010. The cubic root of 21006905 is about 275.9226530093.

Adding to 21006905 its reverse (50960012), we get a palindrome (71966917).

The spelling of 21006905 in words is "twenty-one million, six thousand, nine hundred five".