161721216693 has 12 divisors (see below), whose sum is σ = 233615219968. Its totient is φ = 107805879720.

The previous prime is 161721216659. The next prime is 161721216703. The reversal of 161721216693 is 396612127161.

161721216693 is a `hidden beast` number, since 1 + 617 + 2 + 1 + 21 + 6 + 6 + 9 + 3 = 666.

It is not a de Polignac number, because 161721216693 - 2²⁵ = 161687662261 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (161721216623) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 563605 + ... + 800682.

Almost surely, 2^161721216693 is an apocalyptic number.

It is an amenable number.

161721216693 is a deficient number, since it is larger than the sum of its proper divisors (71894003275).

161721216693 is a wasteful number, since it uses less digits than its factorization.

161721216693 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1377464 (or 1377461 counting only the distinct ones).

The product of its digits is 163296, while the sum is 45.

The spelling of 161721216693 in words is "one hundred sixty-one billion, seven hundred twenty-one million, two hundred sixteen thousand, six hundred ninety-three".