1991385 has 48 divisors (see below), whose sum is σ = 3931200. Its totient is φ = 959040.

The previous prime is 1991359. The next prime is 1991387. The reversal of 1991385 is 5831991.

It is a happy number.

It is not a de Polignac number, because 1991385 - 2¹⁰ = 1990361 is a prime.

It is a super-2 number, since 2×1991385² = 7931228436450, which contains 22 as substring.

It is a Smith number, since the sum of its digits (36) coincides with the sum of the digits of its prime factors.

It is an Ulam number.

Its product of digits (9720) is a multiple of the sum of its prime factors (180).

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 47 ways as a sum of consecutive naturals, for example, 13291 + ... + 13439.

It is an arithmetic number, because the mean of its divisors is an integer number (81900).

2^1991385 is an apocalyptic number.

1991385 is a gapful number since it is divisible by the number (15) formed by its first and last digit.

It is an amenable number.

1991385 is a deficient number, since it is larger than the sum of its proper divisors (1939815).

1991385 is a wasteful number, since it uses less digits than its factorization.

1991385 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 180 (or 168 counting only the distinct ones).

The product of its digits is 9720, while the sum is 36.

The square root of 1991385 is about 1411.1644128166. The cubic root of 1991385 is about 125.8109409545.

Subtracting 1991385 from its reverse (5831991), we obtain a triangular number (3840606 = T₂₇₇₁).

The spelling of 1991385 in words is "one million, nine hundred ninety-one thousand, three hundred eighty-five".