261553170742645 has 4 divisors (see below), whose sum is σ = 313863804891180. Its totient is φ = 209242536594112.

The previous prime is 261553170742637. The next prime is 261553170742687. The reversal of 261553170742645 is 546247071355162.

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 179010458311441 + 82542712431204 = 13379479^2 + 9085302^2 .

It is a cyclic number.

It is not a de Polignac number, because 261553170742645 - 2³ = 261553170742637 is a prime.

It is a super-2 number, since 2×261553170742645² (a number of 30 digits) contains 22 as substring.

It is a Smith number, since the sum of its digits (58) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a self number, because there is not a number n which added to its sum of digits gives 261553170742645.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (31) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 26155317074260 + ... + 26155317074269.

It is an arithmetic number, because the mean of its divisors is an integer number (78465951222795).

Almost surely, 2^{261553170742645} is an apocalyptic number.

It is an amenable number.

261553170742645 is a deficient number, since it is larger than the sum of its proper divisors (52310634148535).

261553170742645 is an equidigital number, since it uses as much as digits as its factorization.

261553170742645 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 52310634148534.

The product of its (nonzero) digits is 42336000, while the sum is 58.

The spelling of 261553170742645 in words is "two hundred sixty-one trillion, five hundred fifty-three billion, one hundred seventy million, seven hundred forty-two thousand, six hundred forty-five".