1991388 has 48 divisors (see below), whose sum is σ = 5379584. Its totient is φ = 561600.

The previous prime is 1991387. The next prime is 1991389. The reversal of 1991388 is 8831991.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (1991387) and next prime (1991389).

It is an Ulam number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1991387) 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, 12606 + ... + 12762.

2^1991388 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 1991388, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (2689792).

1991388 is an abundant number, since it is smaller than the sum of its proper divisors (3388196).

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

1991388 is a wasteful number, since it uses less digits than its factorization.

1991388 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 322 (or 320 counting only the distinct ones).

The product of its digits is 15552, while the sum is 39.

The square root of 1991388 is about 1411.1654757682. The cubic root of 1991388 is about 125.8110041321.

The spelling of 1991388 in words is "one million, nine hundred ninety-one thousand, three hundred eighty-eight".