645161661 has 24 divisors (see below), whose sum is σ = 978434496. Its totient is φ = 408862080.

The previous prime is 645161617. The next prime is 645161683. The reversal of 645161661 is 166161546.

It is a happy number.

645161661 is a `hidden beast` number, since 645 + 1 + 6 + 1 + 6 + 6 + 1 = 666.

It is not a de Polignac number, because 645161661 - 2⁹ = 645161149 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (645161161) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 24181 + ... + 43301.

It is an arithmetic number, because the mean of its divisors is an integer number (40768104).

Almost surely, 2^645161661 is an apocalyptic number.

It is an amenable number.

645161661 is a deficient number, since it is larger than the sum of its proper divisors (333272835).

645161661 is a wasteful number, since it uses less digits than its factorization.

645161661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19313 (or 19310 counting only the distinct ones).

The product of its digits is 25920, while the sum is 36.

The square root of 645161661 is about 25400.0326968293. The cubic root of 645161661 is about 864.0844382818.

The spelling of 645161661 in words is "six hundred forty-five million, one hundred sixty-one thousand, six hundred sixty-one".