2561991 has 8 divisors (see below), whose sum is σ = 3508464. Its totient is φ = 1661760.

The previous prime is 2561987. The next prime is 2562011. The reversal of 2561991 is 1991652.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 2561991 - 2² = 2561987 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (2561921) 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 in 7 ways as a sum of consecutive naturals, for example, 11430 + ... + 11651.

It is an arithmetic number, because the mean of its divisors is an integer number (438558).

2^2561991 is an apocalyptic number.

2561991 is a deficient number, since it is larger than the sum of its proper divisors (946473).

2561991 is a wasteful number, since it uses less digits than its factorization.

2561991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23121.

The product of its digits is 4860, while the sum is 33.

The square root of 2561991 is about 1600.6220665729. The cubic root of 2561991 is about 136.8335307328.

The spelling of 2561991 in words is "two million, five hundred sixty-one thousand, nine hundred ninety-one".