645721471 has 4 divisors (see below), whose sum is σ = 645933600. Its totient is φ = 645509344.

The previous prime is 645721459. The next prime is 645721477. The reversal of 645721471 is 174127546.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 174127546 = 2 ⋅87063773.

It is a cyclic number.

It is not a de Polignac number, because 645721471 - 2¹⁷ = 645590399 is a prime.

It is a super-3 number, since 3×645721471³ (a number of 27 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 645721471.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (645721477) 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, 101431 + ... + 107608.

It is an arithmetic number, because the mean of its divisors is an integer number (161483400).

Almost surely, 2^645721471 is an apocalyptic number.

645721471 is a deficient number, since it is larger than the sum of its proper divisors (212129).

645721471 is a wasteful number, since it uses less digits than its factorization.

645721471 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 212128.

The product of its digits is 47040, while the sum is 37.

The square root of 645721471 is about 25411.0501750715. The cubic root of 645721471 is about 864.3342894930.

The spelling of 645721471 in words is "six hundred forty-five million, seven hundred twenty-one thousand, four hundred seventy-one".