1991780 has 48 divisors (see below), whose sum is σ = 4910976. Its totient is φ = 664320.

The previous prime is 1991779. The next prime is 1991797. The reversal of 1991780 is 871991.

It is a Smith number, since the sum of its digits (35) coincides with the sum of the digits of its prime factors.

It is a Harshad number since it is a multiple of its sum of digits (35).

It is a self number, because there is not a number n which added to its sum of digits gives 1991780.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 5567 + ... + 5913.

It is an arithmetic number, because the mean of its divisors is an integer number (102312).

2^1991780 is an apocalyptic number.

1991780 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 1991780, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (2455488).

1991780 is an abundant number, since it is smaller than the sum of its proper divisors (2919196).

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

1991780 is a wasteful number, since it uses less digits than its factorization.

1991780 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 404 (or 402 counting only the distinct ones).

The product of its (nonzero) digits is 4536, while the sum is 35.

The square root of 1991780 is about 1411.3043612205. The cubic root of 1991780 is about 125.8192587896.

The spelling of 1991780 in words is "one million, nine hundred ninety-one thousand, seven hundred eighty".