645545261 has 4 divisors (see below), whose sum is σ = 653716800. Its totient is φ = 637373724.

The previous prime is 645545207. The next prime is 645545269. The reversal of 645545261 is 162545546.

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: 162545546 = 2 ⋅81272773.

It is a cyclic number.

It is not a de Polignac number, because 645545261 - 2¹⁸ = 645283117 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 (645545269) 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 3 ways as a sum of consecutive naturals, for example, 4085651 + ... + 4085808.

It is an arithmetic number, because the mean of its divisors is an integer number (163429200).

Almost surely, 2^645545261 is an apocalyptic number.

It is an amenable number.

645545261 is a deficient number, since it is larger than the sum of its proper divisors (8171539).

645545261 is an equidigital number, since it uses as much as digits as its factorization.

645545261 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8171538.

The product of its digits is 144000, while the sum is 38.

The square root of 645545261 is about 25407.5827461016. The cubic root of 645545261 is about 864.2556600280.

The spelling of 645545261 in words is "six hundred forty-five million, five hundred forty-five thousand, two hundred sixty-one".