261181561 has 2 divisors, whose sum is σ = 261181562. Its totient is φ = 261181560.

The previous prime is 261181559. The next prime is 261181567. The reversal of 261181561 is 165181162.

261181561 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 256640400 + 4541161 = 16020^2 + 2131^2 .

It is a cyclic number.

It is not a de Polignac number, because 261181561 - 2¹ = 261181559 is a prime.

Together with 261181559, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (261181567) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130590780 + 130590781.

It is an arithmetic number, because the mean of its divisors is an integer number (130590781).

Almost surely, 2^261181561 is an apocalyptic number.

It is an amenable number.

261181561 is a deficient number, since it is larger than the sum of its proper divisors (1).

261181561 is an equidigital number, since it uses as much as digits as its factorization.

261181561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2880, while the sum is 31.

The square root of 261181561 is about 16161.1126164011. The cubic root of 261181561 is about 639.2158046505.

The spelling of 261181561 in words is "two hundred sixty-one million, one hundred eighty-one thousand, five hundred sixty-one".