991209208551 has 8 divisors (see below), whose sum is σ = 1321855645824. Its totient is φ = 660684455160.

The previous prime is 991209208537. The next prime is 991209208559. The reversal of 991209208551 is 155802902199.

It is a happy number.

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

It is not a de Polignac number, because 991209208551 - 2⁶ = 991209208487 is a prime.

It is a Smith number, since the sum of its digits (51) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a junction number, because it is equal to n+sod(n) for n = 991209208494 and 991209208503.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (991209208559) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 30401961 + ... + 30434546.

It is an arithmetic number, because the mean of its divisors is an integer number (165231955728).

Almost surely, 2^991209208551 is an apocalyptic number.

991209208551 is a deficient number, since it is larger than the sum of its proper divisors (330646437273).

991209208551 is a wasteful number, since it uses less digits than its factorization.

991209208551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 60841941.

The product of its (nonzero) digits is 583200, while the sum is 51.

The spelling of 991209208551 in words is "nine hundred ninety-one billion, two hundred nine million, two hundred eight thousand, five hundred fifty-one".