1999 has 2 divisors, whose sum is σ = 2000. Its totient is φ = 1998.

The previous prime is 1997. The next prime is 2003. The reversal of 1999 is 9991.

1999 = T_{35} + T_{36} +
T_{37}.

1999 is nontrivially palindromic in base 6.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 1999 - 2^{1} = 1997 is a prime.

Together with 1997, it forms a pair of twin primes.

It is a fibodiv number, since the Fibonacci-like sequence with seeds 1 and 999 contains 1999 itself.

1999 is an undulating number in base 6.

1999 is a modest number, since divided by 99 gives 19 as remainder.

It is a plaindrome in base 10, base 11 and base 16.

It is a nialpdrome in base 7 and base 13.

It is a zygodrome in base 2.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1993) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 999 + 1000.

It is an arithmetic number, because the mean of its divisors is an integer number (1000).

1999 is the 37-th centered triangular number.

1999 is a deficient number, since it is larger than the sum of its proper divisors (1).

1999 is an equidigital number, since it uses as much as digits as its factorization.

1999 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 729, while the sum is 28.

The square root of 1999 is about 44.7101778122. The cubic root of 1999 is about 12.5971102805.

It can be divided in two parts, 19 and 99, that multiplied together give a palindrome (1881).

The spelling of 1999 in words is "one thousand, nine hundred ninety-nine".

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