1991397 has 8 divisors (see below), whose sum is σ = 2811456. Its totient is φ = 1249472.

The previous prime is 1991389. The next prime is 1991413. The reversal of 1991397 is 7931991.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 1991397 - 2³ = 1991389 is a prime.

1991397 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1991357) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 19473 + ... + 19574.

It is an arithmetic number, because the mean of its divisors is an integer number (351432).

2^1991397 is an apocalyptic number.

1991397 is a gapful number since it is divisible by the number (17) formed by its first and last digit.

It is an amenable number.

1991397 is a deficient number, since it is larger than the sum of its proper divisors (820059).

1991397 is a wasteful number, since it uses less digits than its factorization.

1991397 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 39067.

The product of its digits is 15309, while the sum is 39.

The square root of 1991397 is about 1411.1686646181. The cubic root of 1991397 is about 125.8111936644.

It can be divided in two parts, 199 and 1397, that added together give a triangular number (1596 = T₅₆).

The spelling of 1991397 in words is "one million, nine hundred ninety-one thousand, three hundred ninety-seven".