2551991 has 4 divisors (see below), whose sum is σ = 2748312. Its totient is φ = 2355672.

The previous prime is 2551987. The next prime is 2551999. The reversal of 2551991 is 1991552.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 2551991 - 2² = 2551987 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (2551999) 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 3 ways as a sum of consecutive naturals, for example, 98141 + ... + 98166.

It is an arithmetic number, because the mean of its divisors is an integer number (687078).

2^2551991 is an apocalyptic number.

2551991 is a deficient number, since it is larger than the sum of its proper divisors (196321).

2551991 is a wasteful number, since it uses less digits than its factorization.

2551991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 196320.

The product of its digits is 4050, while the sum is 32.

The square root of 2551991 is about 1597.4952269099. The cubic root of 2551991 is about 136.6552683996.

It can be divided in two parts, 255 and 1991, that multiplied together give a palindrome (507705).

The spelling of 2551991 in words is "two million, five hundred fifty-one thousand, nine hundred ninety-one".