643651081 has 2 divisors, whose sum is σ = 643651082. Its totient is φ = 643651080.

The previous prime is 643651061. The next prime is 643651121. The reversal of 643651081 is 180156346.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 616777225 + 26873856 = 24835^2 + 5184^2 .

It is a cyclic number.

It is not a de Polignac number, because 643651081 - 2¹³ = 643642889 is a prime.

It is a super-2 number, since 2×643651081² = 828573428144937122, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (643651061) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321825540 + 321825541.

It is an arithmetic number, because the mean of its divisors is an integer number (321825541).

Almost surely, 2^643651081 is an apocalyptic number.

It is an amenable number.

643651081 is a deficient number, since it is larger than the sum of its proper divisors (1).

643651081 is an equidigital number, since it uses as much as digits as its factorization.

643651081 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 17280, while the sum is 34.

The square root of 643651081 is about 25370.2794821027. The cubic root of 643651081 is about 863.4095228332.

The spelling of 643651081 in words is "six hundred forty-three million, six hundred fifty-one thousand, eighty-one".