261183345721 has 3 divisors (see below), whose sum is σ = 261183856783. Its totient is φ = 261182834660.

The previous prime is 261183345719. The next prime is 261183345737. The reversal of 261183345721 is 127543381162.

It is a happy number.

The square root of 261183345721 is 511061.

It is a perfect power (a square), and thus also a powerful number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in only one way, i.e., 1022121 + 261182323600 = 1011^2 + 511060^2 .

It is not a de Polignac number, because 261183345721 - 2¹ = 261183345719 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (261183345781) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 255531 + ... + 766591.

Almost surely, 2^261183345721 is an apocalyptic number.

261183345721 is the 511061-st square number.

261183345721 is the 255531-st centered octagonal number.

It is an amenable number.

261183345721 is a deficient number, since it is larger than the sum of its proper divisors (511062).

261183345721 is an frugal number, since it uses more digits than its factorization.

261183345721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1022122 (or 511061 counting only the distinct ones).

The product of its digits is 241920, while the sum is 43.

The spelling of 261183345721 in words is "two hundred sixty-one billion, one hundred eighty-three million, three hundred forty-five thousand, seven hundred twenty-one".