21817582645 has 4 divisors (see below), whose sum is σ = 26181099180. Its totient is φ = 17454066112.

The previous prime is 21817582643. The next prime is 21817582667. The reversal of 21817582645 is 54628571812.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 16471925649 + 5345656996 = 128343^2 + 73114^2 .

It is a cyclic number.

It is not a de Polignac number, because 21817582645 - 2¹ = 21817582643 is a prime.

It is a Smith number, since the sum of its digits (49) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21817582643) 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, 2181758260 + ... + 2181758269.

It is an arithmetic number, because the mean of its divisors is an integer number (6545274795).

Almost surely, 2^21817582645 is an apocalyptic number.

It is an amenable number.

21817582645 is a deficient number, since it is larger than the sum of its proper divisors (4363516535).

21817582645 is an equidigital number, since it uses as much as digits as its factorization.

21817582645 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4363516534.

The product of its digits is 1075200, while the sum is 49.

The spelling of 21817582645 in words is "twenty-one billion, eight hundred seventeen million, five hundred eighty-two thousand, six hundred forty-five".