261115991 has 2 divisors, whose sum is σ = 261115992. Its totient is φ = 261115990.

The previous prime is 261115979. The next prime is 261115997. The reversal of 261115991 is 199511162.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 261115991 - 2⁶ = 261115927 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (261115997) 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, 130557995 + 130557996.

It is an arithmetic number, because the mean of its divisors is an integer number (130557996).

Almost surely, 2^261115991 is an apocalyptic number.

261115991 is a deficient number, since it is larger than the sum of its proper divisors (1).

261115991 is an equidigital number, since it uses as much as digits as its factorization.

261115991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 4860, while the sum is 35.

The square root of 261115991 is about 16159.0838539813. The cubic root of 261115991 is about 639.1623081631.

The spelling of 261115991 in words is "two hundred sixty-one million, one hundred fifteen thousand, nine hundred ninety-one".