1991287 has 4 divisors (see below), whose sum is σ = 2037640. Its totient is φ = 1944936.

The previous prime is 1991281. The next prime is 1991293. The reversal of 1991287 is 7821991.

It is a semiprime because it is the product of two primes.

It is an interprime number because it is at equal distance from previous prime (1991281) and next prime (1991293).

It is a cyclic number.

It is not a de Polignac number, because 1991287 - 2³ = 1991279 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1991281) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 23112 + ... + 23197.

It is an arithmetic number, because the mean of its divisors is an integer number (509410).

2^1991287 is an apocalyptic number.

1991287 is a deficient number, since it is larger than the sum of its proper divisors (46353).

1991287 is an equidigital number, since it uses as much as digits as its factorization.

1991287 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 46352.

The product of its digits is 9072, while the sum is 37.

The square root of 1991287 is about 1411.1296892915. The cubic root of 1991287 is about 125.8088771188.

It can be divided in two parts, 1991 and 287, that added together give a triangular number (2278 = T₆₇).

The spelling of 1991287 in words is "one million, nine hundred ninety-one thousand, two hundred eighty-seven".