261661649 has 2 divisors, whose sum is σ = 261661650. Its totient is φ = 261661648.

The previous prime is 261661633. The next prime is 261661721. The reversal of 261661649 is 946166162.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 225961024 + 35700625 = 15032^2 + 5975^2 .

It is a cyclic number.

It is not a de Polignac number, because 261661649 - 2⁴ = 261661633 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (261661619) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130830824 + 130830825.

It is an arithmetic number, because the mean of its divisors is an integer number (130830825).

Almost surely, 2^261661649 is an apocalyptic number.

It is an amenable number.

261661649 is a deficient number, since it is larger than the sum of its proper divisors (1).

261661649 is an equidigital number, since it uses as much as digits as its factorization.

261661649 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 93312, while the sum is 41.

The square root of 261661649 is about 16175.9589823911. The cubic root of 261661649 is about 639.6072207451.

The spelling of 261661649 in words is "two hundred sixty-one million, six hundred sixty-one thousand, six hundred forty-nine".