1991531 has 4 divisors (see below), whose sum is σ = 2033952. Its totient is φ = 1949112.

The previous prime is 1991527. The next prime is 1991551. The reversal of 1991531 is 1351991.

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

It is a cyclic number.

It is not a de Polignac number, because 1991531 - 2² = 1991527 is a prime.

It is a super-2 number, since 2×1991531² = 7932391447922, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 1991494 and 1991503.

It is not an unprimeable number, because it can be changed into a prime (1991551) 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, 21140 + ... + 21233.

It is an arithmetic number, because the mean of its divisors is an integer number (508488).

2^1991531 is an apocalyptic number.

1991531 is a deficient number, since it is larger than the sum of its proper divisors (42421).

1991531 is an equidigital number, since it uses as much as digits as its factorization.

1991531 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 42420.

The product of its digits is 1215, while the sum is 29.

The square root of 1991531 is about 1411.2161421979. The cubic root of 1991531 is about 125.8140155230.

The spelling of 1991531 in words is "one million, nine hundred ninety-one thousand, five hundred thirty-one".