1991010000 has 400 divisors, whose sum is σ = 7747520000. Its totient is φ = 430272000.

The previous prime is 1991009987. The next prime is 1991010013. The reversal of 1991010000 is 101991.

It is an interprime number because it is at equal distance from previous prime (1991009987) and next prime (1991010013).

It is a tau number, because it is divible by the number of its divisors (400).

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 79 ways as a sum of consecutive naturals, for example, 3989751 + ... + 3990249.

It is an arithmetic number, because the mean of its divisors is an integer number (19368800).

Almost surely, 2^1991010000 is an apocalyptic number.

1991010000 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 1991010000, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (3873760000).

1991010000 is an abundant number, since it is smaller than the sum of its proper divisors (5756510000).

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

1991010000 is a wasteful number, since it uses less digits than its factorization.

1991010000 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 556 (or 535 counting only the distinct ones).

The product of its (nonzero) digits is 81, while the sum is 21.

The square root of 1991010000 is about 44620.7350903142. The cubic root of 1991010000 is about 1258.0304325775.

Adding to 1991010000 its reverse (101991), we get a palindrome (1991111991).

The spelling of 1991010000 in words is "one billion, nine hundred ninety-one million, ten thousand".