1639640921 has 2 divisors, whose sum is σ = 1639640922. Its totient is φ = 1639640920.

The previous prime is 1639640917. The next prime is 1639640941. The reversal of 1639640921 is 1290469361.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1079845321 + 559795600 = 32861^2 + 23660^2 .

It is an emirp because it is prime and its reverse (1290469361) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1639640921 - 2² = 1639640917 is a prime.

It is not a weakly prime, because it can be changed into another prime (1639640941) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 819820460 + 819820461.

It is an arithmetic number, because the mean of its divisors is an integer number (819820461).

Almost surely, 2^1639640921 is an apocalyptic number.

It is an amenable number.

1639640921 is a deficient number, since it is larger than the sum of its proper divisors (1).

1639640921 is an equidigital number, since it uses as much as digits as its factorization.

1639640921 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 69984, while the sum is 41.

The square root of 1639640921 is about 40492.4798079841. The cubic root of 1639640921 is about 1179.1876341460.

The spelling of 1639640921 in words is "one billion, six hundred thirty-nine million, six hundred forty thousand, nine hundred twenty-one".