645139661 has 16 divisors (see below), whose sum is σ = 689438400. Its totient is φ = 601924608.

The previous prime is 645139643. The next prime is 645139687. The reversal of 645139661 is 166931546.

It is a cyclic number.

It is not a de Polignac number, because 645139661 - 2¹⁸ = 644877517 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (645139601) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 909575 + ... + 910283.

It is an arithmetic number, because the mean of its divisors is an integer number (43089900).

Almost surely, 2^645139661 is an apocalyptic number.

It is an amenable number.

645139661 is a deficient number, since it is larger than the sum of its proper divisors (44298739).

645139661 is a wasteful number, since it uses less digits than its factorization.

645139661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1388.

The product of its digits is 116640, while the sum is 41.

The square root of 645139661 is about 25399.5996228287. The cubic root of 645139661 is about 864.0746164160.

The spelling of 645139661 in words is "six hundred forty-five million, one hundred thirty-nine thousand, six hundred sixty-one".