21209706 has 24 divisors (see below), whose sum is σ = 52519584. Its totient is φ = 6059880.

The previous prime is 21209663. The next prime is 21209717. The reversal of 21209706 is 60790212.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21209706.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 84040 + ... + 84291.

It is an arithmetic number, because the mean of its divisors is an integer number (2188316).

Almost surely, 2^21209706 is an apocalyptic number.

21209706 is an abundant number, since it is smaller than the sum of its proper divisors (31309878).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21209706 is a wasteful number, since it uses less digits than its factorization.

21209706 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 168346 (or 168343 counting only the distinct ones).

The product of its (nonzero) digits is 1512, while the sum is 27.

The square root of 21209706 is about 4605.3996569245. The cubic root of 21209706 is about 276.8077314852.

Adding to 21209706 its reverse (60790212), we get a palindrome (81999918).

The spelling of 21209706 in words is "twenty-one million, two hundred nine thousand, seven hundred six".