643542666 has 16 divisors (see below), whose sum is σ = 1386092064. Its totient is φ = 198013104.

The previous prime is 643542643. The next prime is 643542689. The reversal of 643542666 is 666245346.

It is an interprime number because it is at equal distance from previous prime (643542643) and next prime (643542689).

It is a Curzon number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4125196 + ... + 4125351.

It is an arithmetic number, because the mean of its divisors is an integer number (86630754).

Almost surely, 2^643542666 is an apocalyptic number.

643542666 is an abundant number, since it is smaller than the sum of its proper divisors (742549398).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

643542666 is a wasteful number, since it uses less digits than its factorization.

643542666 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8250565.

The product of its digits is 622080, while the sum is 42.

The square root of 643542666 is about 25368.1427384821. The cubic root of 643542666 is about 863.3610432546.

The spelling of 643542666 in words is "six hundred forty-three million, five hundred forty-two thousand, six hundred sixty-six".