261605161 has 2 divisors, whose sum is σ = 261605162. Its totient is φ = 261605160.

The previous prime is 261605159. The next prime is 261605173. The reversal of 261605161 is 161506162.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 238517136 + 23088025 = 15444^2 + 4805^2 .

It is a cyclic number.

It is not a de Polignac number, because 261605161 - 2¹ = 261605159 is a prime.

Together with 261605159, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (261605101) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130802580 + 130802581.

It is an arithmetic number, because the mean of its divisors is an integer number (130802581).

Almost surely, 2^261605161 is an apocalyptic number.

It is an amenable number.

261605161 is a deficient number, since it is larger than the sum of its proper divisors (1).

261605161 is an equidigital number, since it uses as much as digits as its factorization.

261605161 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2160, while the sum is 28.

The square root of 261605161 is about 16174.2128401972. The cubic root of 261605161 is about 639.5611909033.

The spelling of 261605161 in words is "two hundred sixty-one million, six hundred five thousand, one hundred sixty-one".