161783991 has 12 divisors (see below), whose sum is σ = 239388240. Its totient is φ = 105225120.

The previous prime is 161783989. The next prime is 161784061. The reversal of 161783991 is 199387161.

It is not a de Polignac number, because 161783991 - 2¹ = 161783989 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (161783911) 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 11 ways as a sum of consecutive naturals, for example, 218851 + ... + 219588.

It is an arithmetic number, because the mean of its divisors is an integer number (19949020).

Almost surely, 2^161783991 is an apocalyptic number.

161783991 is a deficient number, since it is larger than the sum of its proper divisors (77604249).

161783991 is a wasteful number, since it uses less digits than its factorization.

161783991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 438486 (or 438483 counting only the distinct ones).

The product of its digits is 81648, while the sum is 45.

The square root of 161783991 is about 12719.4335958800. The cubic root of 161783991 is about 544.8937772388.

The spelling of 161783991 in words is "one hundred sixty-one million, seven hundred eighty-three thousand, nine hundred ninety-one".