1991664 has 30 divisors (see below), whose sum is σ = 5574296. Its totient is φ = 663840.

The previous prime is 1991653. The next prime is 1991677. The reversal of 1991664 is 4661991.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a nude number because it is divisible by every one of its digits.

It is a zygodrome in base 2.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 6772 + ... + 7059.

2^1991664 is an apocalyptic number.

It is an amenable number.

1991664 is an abundant number, since it is smaller than the sum of its proper divisors (3582632).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

1991664 is a wasteful number, since it uses less digits than its factorization.

1991664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13845 (or 13836 counting only the distinct ones).

The product of its digits is 11664, while the sum is 36.

The square root of 1991664 is about 1411.2632638881. The cubic root of 1991664 is about 125.8168161977.

The spelling of 1991664 in words is "one million, nine hundred ninety-one thousand, six hundred sixty-four".