261553609 has 2 divisors, whose sum is σ = 261553610. Its totient is φ = 261553608.

The previous prime is 261553597. The next prime is 261553661. The reversal of 261553609 is 906355162.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 209670400 + 51883209 = 14480^2 + 7203^2 .

It is a cyclic number.

It is not a de Polignac number, because 261553609 - 2¹⁵ = 261520841 is a prime.

It is not a weakly prime, because it can be changed into another prime (261553009) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130776804 + 130776805.

It is an arithmetic number, because the mean of its divisors is an integer number (130776805).

Almost surely, 2^261553609 is an apocalyptic number.

It is an amenable number.

261553609 is a deficient number, since it is larger than the sum of its proper divisors (1).

261553609 is an equidigital number, since it uses as much as digits as its factorization.

261553609 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 48600, while the sum is 37.

The square root of 261553609 is about 16172.6191137985. The cubic root of 261553609 is about 639.5191774298.

The spelling of 261553609 in words is "two hundred sixty-one million, five hundred fifty-three thousand, six hundred nine".