1991501 has 4 divisors (see below), whose sum is σ = 2078112. Its totient is φ = 1904892.

The previous prime is 1991491. The next prime is 1991503. The reversal of 1991501 is 1051991.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 1991501 - 2¹⁴ = 1975117 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 (1991503) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 43271 + ... + 43316.

It is an arithmetic number, because the mean of its divisors is an integer number (519528).

2^1991501 is an apocalyptic number.

It is an amenable number.

1991501 is a deficient number, since it is larger than the sum of its proper divisors (86611).

1991501 is an equidigital number, since it uses as much as digits as its factorization.

1991501 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 86610.

The product of its (nonzero) digits is 405, while the sum is 26.

The square root of 1991501 is about 1411.2055130278. The cubic root of 1991501 is about 125.8133837746.

The spelling of 1991501 in words is "one million, nine hundred ninety-one thousand, five hundred one".