261243781 has 4 divisors (see below), whose sum is σ = 262135692. Its totient is φ = 260351872.

The previous prime is 261243779. The next prime is 261243833. The reversal of 261243781 is 187342162.

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 177795556 + 83448225 = 13334^2 + 9135^2 .

It is a cyclic number.

It is not a de Polignac number, because 261243781 - 2¹ = 261243779 is a prime.

It is a super-2 number, since 2×261243781² = 136496626222351922, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (261243701) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 445516 + ... + 446101.

It is an arithmetic number, because the mean of its divisors is an integer number (65533923).

Almost surely, 2^261243781 is an apocalyptic number.

It is an amenable number.

261243781 is a deficient number, since it is larger than the sum of its proper divisors (891911).

261243781 is an equidigital number, since it uses as much as digits as its factorization.

261243781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 891910.

The product of its digits is 16128, while the sum is 34.

The square root of 261243781 is about 16163.0374929962. The cubic root of 261243781 is about 639.2665597005.

The spelling of 261243781 in words is "two hundred sixty-one million, two hundred forty-three thousand, seven hundred eighty-one".