1991977988 has 216 divisors, whose sum is σ = 4906742400. Its totient is φ = 706305600.

The previous prime is 1991977987. The next prime is 1991978033. The reversal of 1991977988 is 8897791991.

Its product of digits (20575296) is a multiple of the sum of its prime factors (144).

It is not an unprimeable number, because it can be changed into a prime (1991977987) by changing a digit.

It is a polite number, since it can be written in 71 ways as a sum of consecutive naturals, for example, 28055993 + ... + 28056063.

It is an arithmetic number, because the mean of its divisors is an integer number (22716400).

Almost surely, 2^1991977988 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 1991977988, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (2453371200).

1991977988 is an abundant number, since it is smaller than the sum of its proper divisors (2914764412).

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

1991977988 is a wasteful number, since it uses less digits than its factorization.

1991977988 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 144 (or 104 counting only the distinct ones).

The product of its digits is 20575296, while the sum is 68.

The square root of 1991977988 is about 44631.5806128351. The cubic root of 1991977988 is about 1258.2342756966.

It can be divided in two parts, 1991 and 977988, that added together give a palindrome (979979).

The spelling of 1991977988 in words is "one billion, nine hundred ninety-one million, nine hundred seventy-seven thousand, nine hundred eighty-eight".