1645907881 has 4 divisors (see below), whose sum is σ = 1646004052. Its totient is φ = 1645811712.

The previous prime is 1645907873. The next prime is 1645907897. The reversal of 1645907881 is 1887095461.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 414529600 + 1231378281 = 20360^2 + 35091^2 .

It is a cyclic number.

It is not a de Polignac number, because 1645907881 - 2³ = 1645907873 is a prime.

It is a super-2 number, since 2×1645907881² = 5418025505475820322, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1645907801) 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, 14676 + ... + 59221.

It is an arithmetic number, because the mean of its divisors is an integer number (411501013).

Almost surely, 2^1645907881 is an apocalyptic number.

It is an amenable number.

1645907881 is a deficient number, since it is larger than the sum of its proper divisors (96171).

1645907881 is an equidigital number, since it uses as much as digits as its factorization.

1645907881 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 96170.

The product of its (nonzero) digits is 483840, while the sum is 49.

The square root of 1645907881 is about 40569.7902508751. The cubic root of 1645907881 is about 1180.6880696871.

The spelling of 1645907881 in words is "one billion, six hundred forty-five million, nine hundred seven thousand, eight hundred eighty-one".