991209208550 has 96 divisors (see below), whose sum is σ = 2016602179200. Its totient is φ = 359482752000.

The previous prime is 991209208537. The next prime is 991209208559. The reversal of 991209208550 is 55802902199.

It is a super-2 number, since 2×991209208550² (a number of 25 digits) contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (50).

Together with 1025392970650 it forms an amicable pair .

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 47 ways as a sum of consecutive naturals, for example, 524726006 + ... + 524727894.

It is an arithmetic number, because the mean of its divisors is an integer number (21006272700).

Almost surely, 2^991209208550 is an apocalyptic number.

991209208550 is the 812900-th pentagonal number.

991209208550 is an abundant number, since it is smaller than the sum of its proper divisors (1025392970650).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

991209208550 is a wasteful number, since it uses less digits than its factorization.

991209208550 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3942 (or 3937 counting only the distinct ones).

The product of its (nonzero) digits is 583200, while the sum is 50.

The spelling of 991209208550 in words is "nine hundred ninety-one billion, two hundred nine million, two hundred eight thousand, five hundred fifty".