1991636640 has 384 divisors, whose sum is σ = 8093675520. Its totient is φ = 447980544.

The previous prime is 1991636611. The next prime is 1991636651. The reversal of 1991636640 is 466361991.

1991636640 is a `hidden beast` number, since 1 + 9 + 9 + 1 + 636 + 6 + 4 + 0 = 666.

It is a super-3 number, since 3×1991636640³ (a number of 29 digits) contains 333 as substring.

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

It is an unprimeable number.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 2025589 + ... + 2026571.

It is an arithmetic number, because the mean of its divisors is an integer number (21077280).

Almost surely, 2^1991636640 is an apocalyptic number.

1991636640 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 1991636640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (4046837760).

1991636640 is an abundant number, since it is smaller than the sum of its proper divisors (6102038880).

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

1991636640 is a wasteful number, since it uses less digits than its factorization.

1991636640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1081 (or 1067 counting only the distinct ones).

The product of its (nonzero) digits is 209952, while the sum is 45.

The square root of 1991636640 is about 44627.7563854604. The cubic root of 1991636640 is about 1258.1624006908.

The spelling of 1991636640 in words is "one billion, nine hundred ninety-one million, six hundred thirty-six thousand, six hundred forty".