261533605665551 has 4 divisors (see below), whose sum is σ = 261533960082600. Its totient is φ = 261533251248504.

The previous prime is 261533605665491. The next prime is 261533605665581. The reversal of 261533605665551 is 155566506335162.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 261533605665551 - 2²⁶ = 261533538556687 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (261533605665581) 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, 176099321 + ... + 177578258.

It is an arithmetic number, because the mean of its divisors is an integer number (65383490020650).

Almost surely, 2^{261533605665551} is an apocalyptic number.

261533605665551 is a deficient number, since it is larger than the sum of its proper divisors (354417049).

261533605665551 is an equidigital number, since it uses as much as digits as its factorization.

261533605665551 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 354417048.

The product of its (nonzero) digits is 72900000, while the sum is 59.

The spelling of 261533605665551 in words is "two hundred sixty-one trillion, five hundred thirty-three billion, six hundred five million, six hundred sixty-five thousand, five hundred fifty-one".