1645661 has 2 divisors, whose sum is σ = 1645662. Its totient is φ = 1645660.

The previous prime is 1645643. The next prime is 1645667. The reversal of 1645661 is 1665461.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1612900 + 32761 = 1270^2 + 181^2 .

It is a cyclic number.

It is not a de Polignac number, because 1645661 - 2¹⁰ = 1644637 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1645667) 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, 822830 + 822831.

It is an arithmetic number, because the mean of its divisors is an integer number (822831).

2^1645661 is an apocalyptic number.

It is an amenable number.

1645661 is a deficient number, since it is larger than the sum of its proper divisors (1).

1645661 is an equidigital number, since it uses as much as digits as its factorization.

1645661 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 4320, while the sum is 29.

The square root of 1645661 is about 1282.8331925858. The cubic root of 1645661 is about 118.0629033571.

The spelling of 1645661 in words is "one million, six hundred forty-five thousand, six hundred sixty-one".