21539909665 has 16 divisors (see below), whose sum is σ = 26094837888. Its totient is φ = 17068029696.

The previous prime is 21539909627. The next prime is 21539909717. The reversal of 21539909665 is 56690993512.

It is a happy number.

It is a cyclic number.

It is not a de Polignac number, because 21539909665 - 2¹⁷ = 21539778593 is a prime.

It is a Duffinian number.

It is an unprimeable number.

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 15 ways as a sum of consecutive naturals, for example, 190729 + ... + 281881.

It is an arithmetic number, because the mean of its divisors is an integer number (1630927368).

Almost surely, 2^21539909665 is an apocalyptic number.

It is an amenable number.

21539909665 is a deficient number, since it is larger than the sum of its proper divisors (4554928223).

21539909665 is a wasteful number, since it uses less digits than its factorization.

21539909665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 91608.

The product of its (nonzero) digits is 3936600, while the sum is 55.

The spelling of 21539909665 in words is "twenty-one billion, five hundred thirty-nine million, nine hundred nine thousand, six hundred sixty-five".