161561 has 2 divisors, whose sum is σ = 161562. Its totient is φ = 161560.

The previous prime is 161543. The next prime is 161563. The reversal of 161561 is 165161.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 144400 + 17161 = 380^2 + 131^2 .

It is an emirp because it is prime and its reverse (165161) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 161561 - 2¹⁴ = 145177 is a prime.

It is a super-2 number, since 2×161561² = 52203913442, which contains 22 as substring.

It is a Sophie Germain prime.

Together with 161563, 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 (161563) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 80780 + 80781.

It is an arithmetic number, because the mean of its divisors is an integer number (80781).

2¹⁶¹⁵⁶¹ is an apocalyptic number.

It is an amenable number.

161561 is a deficient number, since it is larger than the sum of its proper divisors (1).

161561 is an equidigital number, since it uses as much as digits as its factorization.

161561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 180, while the sum is 20.

The square root of 161561 is about 401.9465138548. The cubic root of 161561 is about 54.4643315135.

Subtracting 161561 from its reverse (165161), we obtain a square (3600 = 60²).

It can be divided in two parts, 16 and 1561, that multiplied together give a triangular number (24976 = T₂₂₃).

The spelling of 161561 in words is "one hundred sixty-one thousand, five hundred sixty-one".