1991638 has 8 divisors (see below), whose sum is σ = 3259080. Its totient is φ = 905280.

The previous prime is 1991623. The next prime is 1991641. The reversal of 1991638 is 8361991.

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

It is a junction number, because it is equal to n+sod(n) for n = 1991597 and 1991606.

It is a congruent number.

It is an unprimeable number.

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, 45243 + ... + 45286.

It is an arithmetic number, because the mean of its divisors is an integer number (407385).

2^1991638 is an apocalyptic number.

1991638 is a deficient number, since it is larger than the sum of its proper divisors (1267442).

1991638 is a wasteful number, since it uses less digits than its factorization.

1991638 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 90542.

The product of its digits is 11664, while the sum is 37.

The square root of 1991638 is about 1411.2540522528. The cubic root of 1991638 is about 125.8162687072.

The spelling of 1991638 in words is "one million, nine hundred ninety-one thousand, six hundred thirty-eight".