1666195021 has 2 divisors, whose sum is σ = 1666195022. Its totient is φ = 1666195020.

The previous prime is 1666195019. The next prime is 1666195031. The reversal of 1666195021 is 1205916661.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1541426121 + 124768900 = 39261^2 + 11170^2 .

It is a cyclic number.

It is not a de Polignac number, because 1666195021 - 2¹ = 1666195019 is a prime.

Together with 1666195019, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1666195031) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 833097510 + 833097511.

It is an arithmetic number, because the mean of its divisors is an integer number (833097511).

Almost surely, 2^1666195021 is an apocalyptic number.

It is an amenable number.

1666195021 is a deficient number, since it is larger than the sum of its proper divisors (1).

1666195021 is an equidigital number, since it uses as much as digits as its factorization.

1666195021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 19440, while the sum is 37.

The square root of 1666195021 is about 40819.0521815488. The cubic root of 1666195021 is about 1185.5192513910.

The spelling of 1666195021 in words is "one billion, six hundred sixty-six million, one hundred ninety-five thousand, twenty-one".