643651 has 2 divisors, whose sum is σ = 643652. Its totient is φ = 643650.

The previous prime is 643649. The next prime is 643661. The reversal of 643651 is 156346.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 643651 - 2¹ = 643649 is a prime.

Together with 643649, it forms a pair of twin primes.

It is a nialpdrome in base 15.

It is not a weakly prime, because it can be changed into another prime (643661) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321825 + 321826.

It is an arithmetic number, because the mean of its divisors is an integer number (321826).

2⁶⁴³⁶⁵¹ is an apocalyptic number.

643651 is a deficient number, since it is larger than the sum of its proper divisors (1).

643651 is an equidigital number, since it uses as much as digits as its factorization.

643651 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2160, while the sum is 25.

The square root of 643651 is about 802.2786299036. The cubic root of 643651 is about 86.3409486615.

Adding to 643651 its reverse (156346), we get a palindrome (799997).

The spelling of 643651 in words is "six hundred forty-three thousand, six hundred fifty-one".