1664021 has 2 divisors, whose sum is σ = 1664022. Its totient is φ = 1664020.

The previous prime is 1664017. The next prime is 1664053. The reversal of 1664021 is 1204661.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1661521 + 2500 = 1289^2 + 50^2 .

It is a cyclic number.

It is not a de Polignac number, because 1664021 - 2² = 1664017 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 1663984 and 1664002.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1664071) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 832010 + 832011.

It is an arithmetic number, because the mean of its divisors is an integer number (832011).

2^1664021 is an apocalyptic number.

It is an amenable number.

1664021 is a deficient number, since it is larger than the sum of its proper divisors (1).

1664021 is an equidigital number, since it uses as much as digits as its factorization.

1664021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 288, while the sum is 20.

The square root of 1664021 is about 1289.9693794815. The cubic root of 1664021 is about 118.5003412311.

Adding to 1664021 its reverse (1204661), we get a palindrome (2868682).

It can be divided in two parts, 16640 and 21, that added together give a palindrome (16661).

The spelling of 1664021 in words is "one million, six hundred sixty-four thousand, twenty-one".