1656991 has 4 divisors (see below), whose sum is σ = 1893712. Its totient is φ = 1420272.

The previous prime is 1656979. The next prime is 1656997. The reversal of 1656991 is 1996561.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 1656991 - 2¹⁵ = 1624223 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 1656991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1656997) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 118350 + ... + 118363.

It is an arithmetic number, because the mean of its divisors is an integer number (473428).

2^1656991 is an apocalyptic number.

1656991 is a deficient number, since it is larger than the sum of its proper divisors (236721).

1656991 is an equidigital number, since it uses as much as digits as its factorization.

1656991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 236720.

The product of its digits is 14580, while the sum is 37.

The square root of 1656991 is about 1287.2416245601. The cubic root of 1656991 is about 118.3332292974. Note that the first 3 decimals are identical.

The spelling of 1656991 in words is "one million, six hundred fifty-six thousand, nine hundred ninety-one".