161561381 has 2 divisors, whose sum is σ = 161561382. Its totient is φ = 161561380.

The previous prime is 161561377. The next prime is 161561417. The reversal of 161561381 is 183165161.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 150062500 + 11498881 = 12250^2 + 3391^2 .

It is a cyclic number.

It is not a de Polignac number, because 161561381 - 2² = 161561377 is a prime.

It is a super-2 number, since 2×161561381² = 52204159661254322, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (161561341) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 80780690 + 80780691.

It is an arithmetic number, because the mean of its divisors is an integer number (80780691).

Almost surely, 2^161561381 is an apocalyptic number.

It is an amenable number.

161561381 is a deficient number, since it is larger than the sum of its proper divisors (1).

161561381 is an equidigital number, since it uses as much as digits as its factorization.

161561381 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 4320, while the sum is 32.

The square root of 161561381 is about 12710.6798008604. The cubic root of 161561381 is about 544.6437432684.

The spelling of 161561381 in words is "one hundred sixty-one million, five hundred sixty-one thousand, three hundred eighty-one".