261905591 has 2 divisors, whose sum is σ = 261905592. Its totient is φ = 261905590.

The previous prime is 261905569. The next prime is 261905593. The reversal of 261905591 is 195509162.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 261905591 - 2¹⁴ = 261889207 is a prime.

Together with 261905593, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (261905593) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130952795 + 130952796.

It is an arithmetic number, because the mean of its divisors is an integer number (130952796).

Almost surely, 2^261905591 is an apocalyptic number.

261905591 is a deficient number, since it is larger than the sum of its proper divisors (1).

261905591 is an equidigital number, since it uses as much as digits as its factorization.

261905591 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 24300, while the sum is 38.

The square root of 261905591 is about 16183.4974897270. The cubic root of 261905591 is about 639.8059234124.

The spelling of 261905591 in words is "two hundred sixty-one million, nine hundred five thousand, five hundred ninety-one".