81821738687 has 4 divisors (see below), whose sum is σ = 88115718600. Its totient is φ = 75527758776.

The previous prime is 81821738659. The next prime is 81821738699. The reversal of 81821738687 is 78683712818.

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

It is a cyclic number.

It is not a de Polignac number, because 81821738687 - 2¹⁸ = 81821476543 is a prime.

It is a super-3 number, since 3×81821738687³ (a number of 34 digits) contains 333 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81821738657) 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, 3146989937 + ... + 3146989962.

It is an arithmetic number, because the mean of its divisors is an integer number (22028929650).

Almost surely, 2^81821738687 is an apocalyptic number.

81821738687 is a deficient number, since it is larger than the sum of its proper divisors (6293979913).

81821738687 is a wasteful number, since it uses less digits than its factorization.

81821738687 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6293979912.

The product of its digits is 7225344, while the sum is 59.

The spelling of 81821738687 in words is "eighty-one billion, eight hundred twenty-one million, seven hundred thirty-eight thousand, six hundred eighty-seven".