261251561 has 4 divisors (see below), whose sum is σ = 268312452. Its totient is φ = 254190672.

The previous prime is 261251533. The next prime is 261251581. The reversal of 261251561 is 165152162.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 238393600 + 22857961 = 15440^2 + 4781^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-261251561 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (261251581) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3530390 + ... + 3530463.

It is an arithmetic number, because the mean of its divisors is an integer number (67078113).

Almost surely, 2^261251561 is an apocalyptic number.

It is an amenable number.

261251561 is a deficient number, since it is larger than the sum of its proper divisors (7060891).

261251561 is an equidigital number, since it uses as much as digits as its factorization.

261251561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7060890.

The product of its digits is 3600, while the sum is 29.

The square root of 261251561 is about 16163.2781637884. The cubic root of 261251561 is about 639.2729055542.

The spelling of 261251561 in words is "two hundred sixty-one million, two hundred fifty-one thousand, five hundred sixty-one".