1643697381 has 16 divisors (see below), whose sum is σ = 2225175680. Its totient is φ = 1079127360.

The previous prime is 1643697371. The next prime is 1643697439. The reversal of 1643697381 is 1837963461.

It is a happy number.

It is not a de Polignac number, because 1643697381 - 2³⁰ = 569955557 is a prime.

It is a super-2 number, since 2×1643697381² = 5403482160612518322, which contains 22 as substring.

It is a Smith number, since the sum of its digits (48) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 1643697381.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1643697311) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 41235 + ... + 70623.

It is an arithmetic number, because the mean of its divisors is an integer number (139073480).

Almost surely, 2^1643697381 is an apocalyptic number.

It is an amenable number.

1643697381 is a deficient number, since it is larger than the sum of its proper divisors (581478299).

1643697381 is a wasteful number, since it uses less digits than its factorization.

1643697381 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 29676.

The product of its digits is 653184, while the sum is 48.

The square root of 1643697381 is about 40542.5379200661. The cubic root of 1643697381 is about 1180.1592672604.

The spelling of 1643697381 in words is "one billion, six hundred forty-three million, six hundred ninety-seven thousand, three hundred eighty-one".