161861681 has 2 divisors, whose sum is σ = 161861682. Its totient is φ = 161861680.

The previous prime is 161861671. The next prime is 161861683. The reversal of 161861681 is 186168161.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 152152225 + 9709456 = 12335^2 + 3116^2 .

It is a cyclic number.

It is not a de Polignac number, because 161861681 - 2¹⁴ = 161845297 is a prime.

It is a super-2 number, since 2×161861681² = 52398407552291522, which contains 22 as substring.

It is a Sophie Germain prime.

Together with 161861683, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (161861683) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 80930840 + 80930841.

It is an arithmetic number, because the mean of its divisors is an integer number (80930841).

Almost surely, 2^161861681 is an apocalyptic number.

It is an amenable number.

161861681 is a deficient number, since it is larger than the sum of its proper divisors (1).

161861681 is an equidigital number, since it uses as much as digits as its factorization.

161861681 is an evil number, because the sum of its binary digits is even.

The product of its digits is 13824, while the sum is 38.

The square root of 161861681 is about 12722.4872175216. The cubic root of 161861681 is about 544.9809841021.

The spelling of 161861681 in words is "one hundred sixty-one million, eight hundred sixty-one thousand, six hundred eighty-one".