261293746561 has 3 divisors (see below), whose sum is σ = 261294257731. Its totient is φ = 261293235392.

The previous prime is 261293746529. The next prime is 261293746631. The reversal of 261293746561 is 165647392162.

The square root of 261293746561 is 511169.

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., 252726392961 + 8567353600 = 502719^2 + 92560^2 .

It is not a de Polignac number, because 261293746561 - 2⁵ = 261293746529 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 261293746499 and 261293746508.

It is not an unprimeable number, because it can be changed into a prime (261293746261) 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 in 2 ways as a sum of consecutive naturals, for example, 255585 + ... + 766753.

Almost surely, 2^261293746561 is an apocalyptic number.

261293746561 is the 511169-th square number.

261293746561 is the 255585-th centered octagonal number.

It is an amenable number.

261293746561 is a deficient number, since it is larger than the sum of its proper divisors (511170).

261293746561 is an frugal number, since it uses more digits than its factorization.

261293746561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1022338 (or 511169 counting only the distinct ones).

The product of its digits is 3265920, while the sum is 52.

The spelling of 261293746561 in words is "two hundred sixty-one billion, two hundred ninety-three million, seven hundred forty-six thousand, five hundred sixty-one".