643969 has 2 divisors, whose sum is σ = 643970. Its totient is φ = 643968.

The previous prime is 643961. The next prime is 643991. The reversal of 643969 is 969346.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 640000 + 3969 = 800^2 + 63^2 .

It is a cyclic number.

It is not a de Polignac number, because 643969 - 2³ = 643961 is a prime.

It is a super-2 number, since 2×643969² = 829392145922, which contains 22 as substring.

It is a Chen prime.

It is a d-powerful number, because it can be written as 6 + 4⁴ + 9⁴ + 3¹² + 6⁶ + 9⁵ .

It is not a weakly prime, because it can be changed into another prime (643961) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321984 + 321985.

It is an arithmetic number, because the mean of its divisors is an integer number (321985).

2⁶⁴³⁹⁶⁹ is an apocalyptic number.

It is an amenable number.

643969 is a deficient number, since it is larger than the sum of its proper divisors (1).

643969 is an equidigital number, since it uses as much as digits as its factorization.

643969 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 34992, while the sum is 37.

The square root of 643969 is about 802.4767909416. The cubic root of 643969 is about 86.3551654245.

It can be divided in two parts, 64 and 3969, that multiplied together give a square (254016 = 504²).

The spelling of 643969 in words is "six hundred forty-three thousand, nine hundred sixty-nine".