261981765 has 12 divisors (see below), whose sum is σ = 454101804. Its totient is φ = 139723584.

The previous prime is 261981761. The next prime is 261981767. The reversal of 261981765 is 567189162.

It can be written as a sum of positive squares in 2 ways, for example, as 53670276 + 208311489 = 7326^2 + 14433^2 .

It is not a de Polignac number, because 261981765 - 2² = 261981761 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (45), and also a Moran number because the ratio is a prime number: 5821817 = 261981765 / (2 + 6 + 1 + 9 + 8 + 1 + 7 + 6 + 5).

It is a self number, because there is not a number n which added to its sum of digits gives 261981765.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (261981761) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 2910864 + ... + 2910953.

It is an arithmetic number, because the mean of its divisors is an integer number (37841817).

Almost surely, 2^261981765 is an apocalyptic number.

It is an amenable number.

261981765 is a deficient number, since it is larger than the sum of its proper divisors (192120039).

261981765 is a wasteful number, since it uses less digits than its factorization.

261981765 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5821828 (or 5821825 counting only the distinct ones).

The product of its digits is 181440, while the sum is 45.

The square root of 261981765 is about 16185.8507654062. The cubic root of 261981765 is about 639.8679455734.

The spelling of 261981765 in words is "two hundred sixty-one million, nine hundred eighty-one thousand, seven hundred sixty-five".