261931009 has 2 divisors, whose sum is σ = 261931010. Its totient is φ = 261931008.

The previous prime is 261930989. The next prime is 261931063. The reversal of 261931009 is 900139162.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 259306609 + 2624400 = 16103^2 + 1620^2 .

It is a cyclic number.

It is not a de Polignac number, because 261931009 - 2¹⁹ = 261406721 is a prime.

It is not a weakly prime, because it can be changed into another prime (261931099) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130965504 + 130965505.

It is an arithmetic number, because the mean of its divisors is an integer number (130965505).

It is a Proth number, since it is equal to 15987 ⋅ 2¹⁴ + 1 and 15987 < 2¹⁴.

Almost surely, 2^261931009 is an apocalyptic number.

It is an amenable number.

261931009 is a deficient number, since it is larger than the sum of its proper divisors (1).

261931009 is an equidigital number, since it uses as much as digits as its factorization.

261931009 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2916, while the sum is 31.

The square root of 261931009 is about 16184.2827768178. The cubic root of 261931009 is about 639.8266205153.

The spelling of 261931009 in words is "two hundred sixty-one million, nine hundred thirty-one thousand, nine".