21505166609 has 4 divisors (see below), whose sum is σ = 21544481904. Its totient is φ = 21465851316.

The previous prime is 21505166569. The next prime is 21505166629. The reversal of 21505166609 is 90666150512.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21505166609 - 2²⁰ = 21504118033 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21505166629) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 19656827 + ... + 19657920.

It is an arithmetic number, because the mean of its divisors is an integer number (5386120476).

Almost surely, 2^21505166609 is an apocalyptic number.

It is an amenable number.

21505166609 is a deficient number, since it is larger than the sum of its proper divisors (39315295).

21505166609 is an equidigital number, since it uses as much as digits as its factorization.

21505166609 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 39315294.

The product of its (nonzero) digits is 97200, while the sum is 41.

The spelling of 21505166609 in words is "twenty-one billion, five hundred five million, one hundred sixty-six thousand, six hundred nine".