991811422800 has 960 divisors, whose sum is σ = 4292339558400. Its totient is φ = 214377062400.

The previous prime is 991811422793. The next prime is 991811422807. The reversal of 991811422800 is 8224118199.

It is an interprime number because it is at equal distance from previous prime (991811422793) and next prime (991811422807).

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (991811422807) by changing a digit.

It is a polite number, since it can be written in 191 ways as a sum of consecutive naturals, for example, 38359477 + ... + 38385323.

It is an arithmetic number, because the mean of its divisors is an integer number (4471187040).

Almost surely, 2^991811422800 is an apocalyptic number.

991811422800 is a gapful number since it is divisible by the number (90) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 991811422800, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (2146169779200).

991811422800 is an abundant number, since it is smaller than the sum of its proper divisors (3300528135600).

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

991811422800 is a wasteful number, since it uses less digits than its factorization.

991811422800 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 25921 (or 25904 counting only the distinct ones).

The product of its (nonzero) digits is 82944, while the sum is 45.

The spelling of 991811422800 in words is "nine hundred ninety-one billion, eight hundred eleven million, four hundred twenty-two thousand, eight hundred".