1643771645 has 4 divisors (see below), whose sum is σ = 1972525980. Its totient is φ = 1315017312.

The previous prime is 1643771639. The next prime is 1643771651. The reversal of 1643771645 is 5461773461.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 5461773461 = 1129 ⋅4837709.

It is an interprime number because it is at equal distance from previous prime (1643771639) and next prime (1643771651).

It can be written as a sum of positive squares in 2 ways, for example, as 302307769 + 1341463876 = 17387^2 + 36626^2 .

It is a cyclic number.

It is not a de Polignac number, because 1643771645 - 2⁴ = 1643771629 is a prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 1643771596 and 1643771605.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 164377160 + ... + 164377169.

It is an arithmetic number, because the mean of its divisors is an integer number (493131495).

Almost surely, 2^1643771645 is an apocalyptic number.

It is an amenable number.

1643771645 is a deficient number, since it is larger than the sum of its proper divisors (328754335).

1643771645 is an equidigital number, since it uses as much as digits as its factorization.

1643771645 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 328754334.

The product of its digits is 423360, while the sum is 44.

The square root of 1643771645 is about 40543.4537872639. The cubic root of 1643771645 is about 1180.1770406107.

The spelling of 1643771645 in words is "one billion, six hundred forty-three million, seven hundred seventy-one thousand, six hundred forty-five".