161975781 has 32 divisors (see below), whose sum is σ = 265050240. Its totient is φ = 98152560.

The previous prime is 161975777. The next prime is 161975839. The reversal of 161975781 is 187579161.

It is not a de Polignac number, because 161975781 - 2² = 161975777 is a prime.

It is a super-2 number, since 2×161975781² = 52472307261119922, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (161975731) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 20691 + ... + 27423.

It is an arithmetic number, because the mean of its divisors is an integer number (8282820).

Almost surely, 2^161975781 is an apocalyptic number.

161975781 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

161975781 is a deficient number, since it is larger than the sum of its proper divisors (103074459).

161975781 is an frugal number, since it uses more digits than its factorization.

161975781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6765 (or 6747 counting only the distinct ones).

The product of its digits is 105840, while the sum is 45.

The square root of 161975781 is about 12726.9706136221. The cubic root of 161975781 is about 545.1090105429.

The spelling of 161975781 in words is "one hundred sixty-one million, nine hundred seventy-five thousand, seven hundred eighty-one".