261686549 has 2 divisors, whose sum is σ = 261686550. Its totient is φ = 261686548.

The previous prime is 261686527. The next prime is 261686561. The reversal of 261686549 is 945686162.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 229310449 + 32376100 = 15143^2 + 5690^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-261686549 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (261386549) 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 as a sum of consecutive naturals, namely, 130843274 + 130843275.

It is an arithmetic number, because the mean of its divisors is an integer number (130843275).

Almost surely, 2^261686549 is an apocalyptic number.

It is an amenable number.

261686549 is a deficient number, since it is larger than the sum of its proper divisors (1).

261686549 is an equidigital number, since it uses as much as digits as its factorization.

261686549 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 622080, while the sum is 47.

The square root of 261686549 is about 16176.7286247869. The cubic root of 261686549 is about 639.6275086687.

The spelling of 261686549 in words is "two hundred sixty-one million, six hundred eighty-six thousand, five hundred forty-nine".