1640991 has 8 divisors (see below), whose sum is σ = 2386944. Its totient is φ = 994520.

The previous prime is 1640971. The next prime is 1641007. The reversal of 1640991 is 1990461.

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

It is a cyclic number.

It is not a de Polignac number, because 1640991 - 2⁶ = 1640927 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1640941) 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, 24831 + ... + 24896.

It is an arithmetic number, because the mean of its divisors is an integer number (298368).

2^1640991 is an apocalyptic number.

1640991 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

1640991 is a deficient number, since it is larger than the sum of its proper divisors (745953).

1640991 is a wasteful number, since it uses less digits than its factorization.

1640991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 49741.

The product of its (nonzero) digits is 1944, while the sum is 30.

The square root of 1640991 is about 1281.0117095484. The cubic root of 1640991 is about 117.9511192736.

Subtracting from 1640991 its sum of digits (30), we obtain a square (1640961 = 1281²).

The spelling of 1640991 in words is "one million, six hundred forty thousand, nine hundred ninety-one".