1991640 has 64 divisors (see below), whose sum is σ = 6831360. Its totient is φ = 455040.

The previous prime is 1991623. The next prime is 1991641. The reversal of 1991640 is 461991.

It is a hoax number, since the sum of its digits (30) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a junction number, because it is equal to n+sod(n) for n = 1991598 and 1991607.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1991641) 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, 346 + ... + 2025.

It is an arithmetic number, because the mean of its divisors is an integer number (106740).

2^1991640 is an apocalyptic number.

1991640 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 1991640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (3415680).

1991640 is an abundant number, since it is smaller than the sum of its proper divisors (4839720).

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

1991640 is a wasteful number, since it uses less digits than its factorization.

1991640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2392 (or 2388 counting only the distinct ones).

The product of its (nonzero) digits is 1944, while the sum is 30.

The square root of 1991640 is about 1411.2547608423. The cubic root of 1991640 is about 125.8163108220.

The spelling of 1991640 in words is "one million, nine hundred ninety-one thousand, six hundred forty".