1991081541600 has 576 divisors, whose sum is σ = 7303887521280. Its totient is φ = 529943109120.

The previous prime is 1991081541577. The next prime is 1991081541661. The reversal of 1991081541600 is 61451801991.

1991081541600 is a `hidden beast` number, since 1 + 99 + 10 + 8 + 1 + 541 + 6 + 0 + 0 = 666.

It is a super-3 number, since 3×1991081541600³ (a number of 38 digits) contains 333 as substring.

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

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 1551894559 + ... + 1551895841.

It is an arithmetic number, because the mean of its divisors is an integer number (12680360280).

Almost surely, 2^{1991081541600} is an apocalyptic number.

1991081541600 is a gapful number since it is divisible by the number (10) 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 1991081541600, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (3651943760640).

1991081541600 is an abundant number, since it is smaller than the sum of its proper divisors (5312805979680).

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

1991081541600 is an equidigital number, since it uses as much as digits as its factorization.

1991081541600 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2211 (or 2180 counting only the distinct ones).

The product of its (nonzero) digits is 77760, while the sum is 45.

The spelling of 1991081541600 in words is "one trillion, nine hundred ninety-one billion, eighty-one million, five hundred forty-one thousand, six hundred".