1991335440 has 80 divisors (see below), whose sum is σ = 6205602816. Its totient is φ = 528230400.

The previous prime is 1991335429. The next prime is 1991335447. The reversal of 1991335440 is 445331991.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (80).

It is not an unprimeable number, because it can be changed into a prime (1991335447) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 24120 + ... + 67560.

Almost surely, 2^1991335440 is an apocalyptic number.

1991335440 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 1991335440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (3102801408).

1991335440 is an abundant number, since it is smaller than the sum of its proper divisors (4214267376).

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

1991335440 is a wasteful number, since it uses less digits than its factorization.

1991335440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 43648 (or 43642 counting only the distinct ones).

The product of its (nonzero) digits is 58320, while the sum is 39.

The square root of 1991335440 is about 44624.3816763885. The cubic root of 1991335440 is about 1258.0989725177.

It can be divided in two parts, 1991 and 335440, that added together give a triangular number (337431 = T₈₂₁).

The spelling of 1991335440 in words is "one billion, nine hundred ninety-one million, three hundred thirty-five thousand, four hundred forty".