161315981 has 2 divisors, whose sum is σ = 161315982. Its totient is φ = 161315980.

The previous prime is 161315977. The next prime is 161316007. The reversal of 161315981 is 189513161.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 135722500 + 25593481 = 11650^2 + 5059^2 .

It is a cyclic number.

It is not a de Polignac number, because 161315981 - 2² = 161315977 is a prime.

It is a super-2 number, since 2×161315981² = 52045691451984722, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (161315881) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 80657990 + 80657991.

It is an arithmetic number, because the mean of its divisors is an integer number (80657991).

Almost surely, 2^161315981 is an apocalyptic number.

It is an amenable number.

161315981 is a deficient number, since it is larger than the sum of its proper divisors (1).

161315981 is an equidigital number, since it uses as much as digits as its factorization.

161315981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 6480, while the sum is 35.

The square root of 161315981 is about 12701.0228328273. The cubic root of 161315981 is about 544.3678454394.

The spelling of 161315981 in words is "one hundred sixty-one million, three hundred fifteen thousand, nine hundred eighty-one".