15551991 has 48 divisors (see below), whose sum is σ = 29300544. Its totient is φ = 7713792.

The previous prime is 15551989. The next prime is 15551999. The reversal of 15551991 is 19915551.

15551991 is a `hidden beast` number, since 1 + 55 + 519 + 91 = 666.

It is not a de Polignac number, because 15551991 - 2¹ = 15551989 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (15551999) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 13365 + ... + 14481.

It is an arithmetic number, because the mean of its divisors is an integer number (610428).

Almost surely, 2^15551991 is an apocalyptic number.

15551991 is a deficient number, since it is larger than the sum of its proper divisors (13748553).

15551991 is a wasteful number, since it uses less digits than its factorization.

15551991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1160 (or 1157 counting only the distinct ones).

The product of its digits is 10125, while the sum is 36.

The square root of 15551991 is about 3943.6012729484. The cubic root of 15551991 is about 249.6100106161.

The spelling of 15551991 in words is "fifteen million, five hundred fifty-one thousand, nine hundred ninety-one".