1991945 has 8 divisors (see below), whose sum is σ = 2400840. Its totient is φ = 1586560.

The previous prime is 1991933. The next prime is 1991947. The reversal of 1991945 is 5491991.

It can be written as a sum of positive squares in 4 ways, for example, as 1024 + 1990921 = 32^2 + 1411^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 1991945 - 2⁴ = 1991929 is a prime.

It is an Ulam number.

It is a junction number, because it is equal to n+sod(n) for n = 1991899 and 1991908.

It is not an unprimeable number, because it can be changed into a prime (1991947) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 605 + ... + 2085.

It is an arithmetic number, because the mean of its divisors is an integer number (300105).

2^1991945 is an apocalyptic number.

It is an amenable number.

1991945 is a deficient number, since it is larger than the sum of its proper divisors (408895).

1991945 is a wasteful number, since it uses less digits than its factorization.

1991945 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1755.

The product of its digits is 14580, while the sum is 38.

The square root of 1991945 is about 1411.3628165713. The cubic root of 1991945 is about 125.8227330027.

The spelling of 1991945 in words is "one million, nine hundred ninety-one thousand, nine hundred forty-five".