21508449209 has 4 divisors (see below), whose sum is σ = 23162945316. Its totient is φ = 19853953104.

The previous prime is 21508449173. The next prime is 21508449239. The reversal of 21508449209 is 90294480512.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 2507205184 + 19001244025 = 50072^2 + 137845^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21508449209 is a prime.

It is a super-2 number, since 2×21508449209² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21508449209.

It is not an unprimeable number, because it can be changed into a prime (21508449239) 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, 827248034 + ... + 827248059.

It is an arithmetic number, because the mean of its divisors is an integer number (5790736329).

Almost surely, 2^21508449209 is an apocalyptic number.

It is an amenable number.

21508449209 is a deficient number, since it is larger than the sum of its proper divisors (1654496107).

21508449209 is a wasteful number, since it uses less digits than its factorization.

21508449209 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1654496106.

The product of its (nonzero) digits is 207360, while the sum is 44.

The spelling of 21508449209 in words is "twenty-one billion, five hundred eight million, four hundred forty-nine thousand, two hundred nine".