161813981 has 4 divisors (see below), whose sum is σ = 184930272. Its totient is φ = 138697692.

The previous prime is 161813963. The next prime is 161814011. The reversal of 161813981 is 189318161.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 189318161 = 271 ⋅698591.

It is a de Polignac number, because none of the positive numbers 2^k-161813981 is a prime.

It is a super-4 number, since 4×161813981⁴ (a number of 34 digits) contains 4444 as substring. Note that it is a super-d number also for d = 2.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (161813941) 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, 11558135 + ... + 11558148.

It is an arithmetic number, because the mean of its divisors is an integer number (46232568).

Almost surely, 2^161813981 is an apocalyptic number.

It is an amenable number.

161813981 is a deficient number, since it is larger than the sum of its proper divisors (23116291).

161813981 is an equidigital number, since it uses as much as digits as its factorization.

161813981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23116290.

The product of its digits is 10368, while the sum is 38.

The square root of 161813981 is about 12720.6124459477. The cubic root of 161813981 is about 544.9274442591.

The spelling of 161813981 in words is "one hundred sixty-one million, eight hundred thirteen thousand, nine hundred eighty-one".