21206705 has 8 divisors (see below), whose sum is σ = 27405672. Its totient is φ = 15660288.

The previous prime is 21206699. The next prime is 21206747. The reversal of 21206705 is 50760212.

It can be written as a sum of positive squares in 4 ways, for example, as 703921 + 20502784 = 839^2 + 4528^2 .

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 21206705 - 2¹² = 21202609 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 163064 + ... + 163193.

It is an arithmetic number, because the mean of its divisors is an integer number (3425709).

Almost surely, 2^21206705 is an apocalyptic number.

It is an amenable number.

21206705 is a deficient number, since it is larger than the sum of its proper divisors (6198967).

21206705 is a wasteful number, since it uses less digits than its factorization.

21206705 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 326275.

The product of its (nonzero) digits is 840, while the sum is 23.

The square root of 21206705 is about 4605.0738321986. The cubic root of 21206705 is about 276.7946755257.

Adding to 21206705 its reverse (50760212), we get a palindrome (71966917).

The spelling of 21206705 in words is "twenty-one million, two hundred six thousand, seven hundred five".