991999550 has 12 divisors (see below), whose sum is σ = 1845119256. Its totient is φ = 396799800.

The previous prime is 991999543. The next prime is 991999559. The reversal of 991999550 is 55999199.

It is a hoax number, since the sum of its digits (56) coincides with the sum of the digits of its distinct prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (991999559) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 9919946 + ... + 9920045.

It is an arithmetic number, because the mean of its divisors is an integer number (153759938).

Almost surely, 2^991999550 is an apocalyptic number.

991999550 is a deficient number, since it is larger than the sum of its proper divisors (853119706).

991999550 is a wasteful number, since it uses less digits than its factorization.

991999550 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19840003 (or 19839998 counting only the distinct ones).

The product of its (nonzero) digits is 1476225, while the sum is 56.

The square root of 991999550 is about 31496.0243522893. The cubic root of 991999550 is about 997.3260396423.

The spelling of 991999550 in words is "nine hundred ninety-one million, nine hundred ninety-nine thousand, five hundred fifty".