21661699809909 has 24 divisors (see below), whose sum is σ = 31069531135360. Its totient is φ = 13419608477184.

The previous prime is 21661699809857. The next prime is 21661699809917. The reversal of 21661699809909 is 90990899616612.

It is not a de Polignac number, because 21661699809909 - 2³³ = 21653109875317 is a prime.

It is a super-2 number, since 2×21661699809909² (a number of 27 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21661699808909) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 158062264 + ... + 158199249.

Almost surely, 2^{21661699809909} is an apocalyptic number.

It is an amenable number.

21661699809909 is a deficient number, since it is larger than the sum of its proper divisors (9407831325451).

21661699809909 is a wasteful number, since it uses less digits than its factorization.

21661699809909 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 316261629 (or 316261612 counting only the distinct ones).

The product of its (nonzero) digits is 204073344, while the sum is 75.

The spelling of 21661699809909 in words is "twenty-one trillion, six hundred sixty-one billion, six hundred ninety-nine million, eight hundred nine thousand, nine hundred nine".