1645742809 has 4 divisors (see below), whose sum is σ = 1656641920. Its totient is φ = 1634843700.

The previous prime is 1645742797. The next prime is 1645742821. The reversal of 1645742809 is 9082475461.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 9082475461 = 29 ⋅313188809.

It is an interprime number because it is at equal distance from previous prime (1645742797) and next prime (1645742821).

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1645742809 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1645740809) 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, 5449329 + ... + 5449630.

It is an arithmetic number, because the mean of its divisors is an integer number (414160480).

Almost surely, 2^1645742809 is an apocalyptic number.

It is an amenable number.

1645742809 is a deficient number, since it is larger than the sum of its proper divisors (10899111).

1645742809 is a wasteful number, since it uses less digits than its factorization.

1645742809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10899110.

The product of its (nonzero) digits is 483840, while the sum is 46.

The square root of 1645742809 is about 40567.7557796830. The cubic root of 1645742809 is about 1180.6485970331.

The spelling of 1645742809 in words is "one billion, six hundred forty-five million, seven hundred forty-two thousand, eight hundred nine".