261813921 has 4 divisors (see below), whose sum is σ = 349085232. Its totient is φ = 174542612.

The previous prime is 261813919. The next prime is 261813931. The reversal of 261813921 is 129318162.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 261813921 - 2¹ = 261813919 is a prime.

It is not an unprimeable number, because it can be changed into a prime (261813911) 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 3 ways as a sum of consecutive naturals, for example, 43635651 + ... + 43635656.

It is an arithmetic number, because the mean of its divisors is an integer number (87271308).

Almost surely, 2^261813921 is an apocalyptic number.

It is an amenable number.

261813921 is a deficient number, since it is larger than the sum of its proper divisors (87271311).

261813921 is an equidigital number, since it uses as much as digits as its factorization.

261813921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 87271310.

The product of its digits is 5184, while the sum is 33.

The square root of 261813921 is about 16180.6650357765. The cubic root of 261813921 is about 639.7312681992.

The spelling of 261813921 in words is "two hundred sixty-one million, eight hundred thirteen thousand, nine hundred twenty-one".