1643078681 has 4 divisors (see below), whose sum is σ = 1643296692. Its totient is φ = 1642860672.

The previous prime is 1643078641. The next prime is 1643078683. The reversal of 1643078681 is 1868703461.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 83539600 + 1559539081 = 9140^2 + 39491^2 .

It is a cyclic number.

It is not a de Polignac number, because 1643078681 - 2¹⁸ = 1642816537 is a prime.

It is a super-2 number, since 2×1643078681² = 5399415103913399522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1643078683) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 97280 + ... + 112913.

It is an arithmetic number, because the mean of its divisors is an integer number (410824173).

Almost surely, 2^1643078681 is an apocalyptic number.

It is an amenable number.

1643078681 is a deficient number, since it is larger than the sum of its proper divisors (218011).

1643078681 is an equidigital number, since it uses as much as digits as its factorization.

1643078681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 218010.

The product of its (nonzero) digits is 193536, while the sum is 44.

The square root of 1643078681 is about 40534.9069445090. The cubic root of 1643078681 is about 1180.0111750833.

The spelling of 1643078681 in words is "one billion, six hundred forty-three million, seventy-eight thousand, six hundred eighty-one".