643649 has 2 divisors, whose sum is σ = 643650. Its totient is φ = 643648.

The previous prime is 643639. The next prime is 643651. The reversal of 643649 is 946346.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 577600 + 66049 = 760^2 + 257^2 .

It is a cyclic number.

It is not a de Polignac number, because 643649 - 2⁴ = 643633 is a prime.

Together with 643651, it forms a pair of twin primes.

It is a Chen prime.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 643649.

It is not a weakly prime, because it can be changed into another prime (643619) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321824 + 321825.

It is an arithmetic number, because the mean of its divisors is an integer number (321825).

2⁶⁴³⁶⁴⁹ is an apocalyptic number.

It is an amenable number.

643649 is a deficient number, since it is larger than the sum of its proper divisors (1).

643649 is an equidigital number, since it uses as much as digits as its factorization.

643649 is an evil number, because the sum of its binary digits is even.

The product of its digits is 15552, while the sum is 32.

The square root of 643649 is about 802.2773834529. The cubic root of 643649 is about 86.3408592331.

The spelling of 643649 in words is "six hundred forty-three thousand, six hundred forty-nine".