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1691 = 1989

1691 has 4 divisors (see below), whose sum is σ = 1800. Its totient is φ = 1584.

The previous prime is 1669. The next prime is 1693. The reversal of 1691 is 1961.

1691 is nontrivially palindromic in base 12.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 1961 = 3753.

It is a cyclic number.

It is not a de Polignac number, because 1691 - 26 = 1627 is a prime.

1691 is a strobogrammatic number because it is the same when read upside-down.

It is a Duffinian number.

1691 is an undulating number in base 12.

It is a plaindrome in base 6, base 9, base 14, base 15 and base 16.

It is not an unprimeable number, because it can be changed into a prime (1693) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 26 + ... + 63.

It is an arithmetic number, because the mean of its divisors is an integer number (450).

1691 is a deficient number, since it is larger than the sum of its proper divisors (109).

1691 is an equidigital number, since it uses as much as digits as its factorization.

1691 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 108.

The product of its digits is 54, while the sum is 17.

The square root of 1691 is about 41.1217703899. The cubic root of 1691 is about 11.9137331742.

The spelling of 1691 in words is "one thousand, six hundred ninety-one".

Divisors: 1 19 89 1691