1999661 has 2 divisors, whose sum is σ = 1999662. Its totient is φ = 1999660.

The previous prime is 1999651. The next prime is 1999667. The reversal of 1999661 is 1669991.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1755625 + 244036 = 1325^2 + 494^2 .

It is a cyclic number.

It is not a de Polignac number, because 1999661 - 2¹⁰ = 1998637 is a prime.

It is a super-2 number, since 2×1999661² = 7997288229842, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1999667) 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 as a sum of consecutive naturals, namely, 999830 + 999831.

It is an arithmetic number, because the mean of its divisors is an integer number (999831).

2^1999661 is an apocalyptic number.

It is an amenable number.

1999661 is a deficient number, since it is larger than the sum of its proper divisors (1).

1999661 is an equidigital number, since it uses as much as digits as its factorization.

1999661 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 26244, while the sum is 41.

The square root of 1999661 is about 1414.0937026944. The cubic root of 1999661 is about 125.9849860333.

The spelling of 1999661 in words is "one million, nine hundred ninety-nine thousand, six hundred sixty-one".