161909731 has 4 divisors (see below), whose sum is σ = 161935200. Its totient is φ = 161884264.

The previous prime is 161909729. The next prime is 161909771. The reversal of 161909731 is 137909161.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 137909161 = 13 ⋅10608397.

It is a cyclic number.

It is not a de Polignac number, because 161909731 - 2¹ = 161909729 is a prime.

It is a super-2 number, since 2×161909731² = 52429521984984722, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (161909771) 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, 5625 + ... + 18853.

It is an arithmetic number, because the mean of its divisors is an integer number (40483800).

Almost surely, 2^161909731 is an apocalyptic number.

161909731 is a deficient number, since it is larger than the sum of its proper divisors (25469).

161909731 is a wasteful number, since it uses less digits than its factorization.

161909731 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 25468.

The product of its (nonzero) digits is 10206, while the sum is 37.

The square root of 161909731 is about 12724.3754660101. The cubic root of 161909731 is about 545.0349061614.

It can be divided in two parts, 16190 and 9731, that added together give a square (25921 = 161²).

The spelling of 161909731 in words is "one hundred sixty-one million, nine hundred nine thousand, seven hundred thirty-one".