261504721 has 4 divisors (see below), whose sum is σ = 262109092. Its totient is φ = 260900352.

The previous prime is 261504709. The next prime is 261504739. The reversal of 261504721 is 127405162.

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 19360000 + 242144721 = 4400^2 + 15561^2 .

It is a cyclic number.

It is not a de Polignac number, because 261504721 - 2⁹ = 261504209 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 261504721.

It is not an unprimeable number, because it can be changed into a prime (261504701) 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, 301536 + ... + 302401.

It is an arithmetic number, because the mean of its divisors is an integer number (65527273).

Almost surely, 2^261504721 is an apocalyptic number.

It is an amenable number.

261504721 is a deficient number, since it is larger than the sum of its proper divisors (604371).

261504721 is an equidigital number, since it uses as much as digits as its factorization.

261504721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 604370.

The product of its (nonzero) digits is 3360, while the sum is 28.

The square root of 261504721 is about 16171.1075996668. The cubic root of 261504721 is about 639.4793299433.

Adding to 261504721 its reverse (127405162), we get a palindrome (388909883).

The spelling of 261504721 in words is "two hundred sixty-one million, five hundred four thousand, seven hundred twenty-one".