261861262720021 has 4 divisors (see below), whose sum is σ = 277264866409452. Its totient is φ = 246457659030592.

The previous prime is 261861262719977. The next prime is 261861262720037. The reversal of 261861262720021 is 120027262168162.

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 218633780512900 + 43227482207121 = 14786270^2 + 6574761^2 .

It is a cyclic number.

It is not a de Polignac number, because 261861262720021 - 2⁹ = 261861262719509 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 (261861262720121) 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, 7701801844690 + ... + 7701801844723.

It is an arithmetic number, because the mean of its divisors is an integer number (69316216602363).

Almost surely, 2^{261861262720021} is an apocalyptic number.

It is an amenable number.

261861262720021 is a deficient number, since it is larger than the sum of its proper divisors (15403603689431).

261861262720021 is a wasteful number, since it uses less digits than its factorization.

261861262720021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15403603689430.

The product of its (nonzero) digits is 387072, while the sum is 46.

The spelling of 261861262720021 in words is "two hundred sixty-one trillion, eight hundred sixty-one billion, two hundred sixty-two million, seven hundred twenty thousand, twenty-one".