1645587721 has 2 divisors, whose sum is σ = 1645587722. Its totient is φ = 1645587720.

The previous prime is 1645587659. The next prime is 1645587731. The reversal of 1645587721 is 1277855461.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1287015625 + 358572096 = 35875^2 + 18936^2 .

It is a cyclic number.

It is not a de Polignac number, because 1645587721 - 2²⁹ = 1108716809 is a prime.

It is not a weakly prime, because it can be changed into another prime (1645587731) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 822793860 + 822793861.

It is an arithmetic number, because the mean of its divisors is an integer number (822793861).

Almost surely, 2^1645587721 is an apocalyptic number.

It is an amenable number.

1645587721 is a deficient number, since it is larger than the sum of its proper divisors (1).

1645587721 is an equidigital number, since it uses as much as digits as its factorization.

1645587721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 470400, while the sum is 46.

The square root of 1645587721 is about 40565.8442658353. The cubic root of 1645587721 is about 1180.6115093868.

The spelling of 1645587721 in words is "one billion, six hundred forty-five million, five hundred eighty-seven thousand, seven hundred twenty-one".