1664123221 has 2 divisors, whose sum is σ = 1664123222. Its totient is φ = 1664123220.

The previous prime is 1664123207. The next prime is 1664123243. The reversal of 1664123221 is 1223214661.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1385700625 + 278422596 = 37225^2 + 16686^2 .

It is a cyclic number.

It is not a de Polignac number, because 1664123221 - 2¹³ = 1664115029 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 1664123221.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1664127221) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 832061610 + 832061611.

It is an arithmetic number, because the mean of its divisors is an integer number (832061611).

Almost surely, 2^1664123221 is an apocalyptic number.

It is an amenable number.

1664123221 is a deficient number, since it is larger than the sum of its proper divisors (1).

1664123221 is an equidigital number, since it uses as much as digits as its factorization.

1664123221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3456, while the sum is 28.

The square root of 1664123221 is about 40793.6664324255. Note that the first 3 decimals coincide. The cubic root of 1664123221 is about 1185.0276767794.

Adding to 1664123221 its reverse (1223214661), we get a palindrome (2887337882).

The spelling of 1664123221 in words is "one billion, six hundred sixty-four million, one hundred twenty-three thousand, two hundred twenty-one".