5551991 has 4 divisors (see below), whose sum is σ = 5587512. Its totient is φ = 5516472.

The previous prime is 5551981. The next prime is 5551999. The reversal of 5551991 is 1991555.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1991555 = 5 ⋅398311.

It is a cyclic number.

It is not a de Polignac number, because 5551991 - 2⁶ = 5551927 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 (5551999) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 17525 + ... + 17838.

It is an arithmetic number, because the mean of its divisors is an integer number (1396878).

Almost surely, 2^5551991 is an apocalyptic number.

5551991 is a deficient number, since it is larger than the sum of its proper divisors (35521).

5551991 is a wasteful number, since it uses less digits than its factorization.

5551991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 35520.

The product of its digits is 10125, while the sum is 35.

The square root of 5551991 is about 2356.2663262034. The cubic root of 5551991 is about 177.0718743712.

The spelling of 5551991 in words is "five million, five hundred fifty-one thousand, nine hundred ninety-one".