1991565 has 12 divisors (see below), whose sum is σ = 3452124. Its totient is φ = 1062144.

The previous prime is 1991551. The next prime is 1991573. The reversal of 1991565 is 5651991.

1991565 is a `hidden beast` number, since 1 + 9 + 91 + 565 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 1397124 + 594441 = 1182^2 + 771^2 .

It is not a de Polignac number, because 1991565 - 2¹¹ = 1989517 is a prime.

It is a super-2 number, since 2×1991565² = 7932662298450, which contains 22 as substring.

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 22084 + ... + 22173.

It is an arithmetic number, because the mean of its divisors is an integer number (287677).

2^1991565 is an apocalyptic number.

1991565 is a gapful number since it is divisible by the number (15) formed by its first and last digit.

It is an amenable number.

1991565 is a deficient number, since it is larger than the sum of its proper divisors (1460559).

1991565 is a wasteful number, since it uses less digits than its factorization.

1991565 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 44268 (or 44265 counting only the distinct ones).

The product of its digits is 12150, while the sum is 36.

The square root of 1991565 is about 1411.2281884940. The cubic root of 1991565 is about 125.8147314968.

It can be divided in two parts, 1991 and 565, that added together give a triangular number (2556 = T₇₁).

The spelling of 1991565 in words is "one million, nine hundred ninety-one thousand, five hundred sixty-five".