81639867651 has 4 divisors (see below), whose sum is σ = 108853156872. Its totient is φ = 54426578432.

The previous prime is 81639867637. The next prime is 81639867671. The reversal of 81639867651 is 15676893618.

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 81639867651 - 2⁷ = 81639867523 is a prime.

It is not an unprimeable number, because it can be changed into a prime (81639867671) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 13606644606 + ... + 13606644611.

It is an arithmetic number, because the mean of its divisors is an integer number (27213289218).

Almost surely, 2^81639867651 is an apocalyptic number.

81639867651 is a deficient number, since it is larger than the sum of its proper divisors (27213289221).

81639867651 is a wasteful number, since it uses less digits than its factorization.

81639867651 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27213289220.

The product of its digits is 13063680, while the sum is 60.

The spelling of 81639867651 in words is "eighty-one billion, six hundred thirty-nine million, eight hundred sixty-seven thousand, six hundred fifty-one".