1640634221 has 2 divisors, whose sum is σ = 1640634222. Its totient is φ = 1640634220.

The previous prime is 1640634209. The next prime is 1640634227. The reversal of 1640634221 is 1224360461.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1189284196 + 451350025 = 34486^2 + 21245^2 .

It is an emirp because it is prime and its reverse (1224360461) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1640634221 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1640634227) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 820317110 + 820317111.

It is an arithmetic number, because the mean of its divisors is an integer number (820317111).

Almost surely, 2^1640634221 is an apocalyptic number.

It is an amenable number.

1640634221 is a deficient number, since it is larger than the sum of its proper divisors (1).

1640634221 is an equidigital number, since it uses as much as digits as its factorization.

1640634221 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 6912, while the sum is 29.

The square root of 1640634221 is about 40504.7431913844. The cubic root of 1640634221 is about 1179.4257046931.

Adding to 1640634221 its reverse (1224360461), we get a palindrome (2864994682).

The spelling of 1640634221 in words is "one billion, six hundred forty million, six hundred thirty-four thousand, two hundred twenty-one".