645812906781 has 16 divisors (see below), whose sum is σ = 984156269184. Its totient is φ = 369013292544.

The previous prime is 645812906747. The next prime is 645812906797. The reversal of 645812906781 is 187609218546.

It is not a de Polignac number, because 645812906781 - 2¹¹ = 645812904733 is a prime.

It is a super-2 number, since 2×645812906781² (a number of 24 digits) contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (645812906281) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 590616 + ... + 1280801.

It is an arithmetic number, because the mean of its divisors is an integer number (61509766824).

Almost surely, 2^645812906781 is an apocalyptic number.

It is an amenable number.

645812906781 is a deficient number, since it is larger than the sum of its proper divisors (338343362403).

645812906781 is a wasteful number, since it uses less digits than its factorization.

645812906781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1887860.

The product of its (nonzero) digits is 5806080, while the sum is 57.

The spelling of 645812906781 in words is "six hundred forty-five billion, eight hundred twelve million, nine hundred six thousand, seven hundred eighty-one".