81635804321 has 4 divisors (see below), whose sum is σ = 81667959600. Its totient is φ = 81603649044.

The previous prime is 81635804303. The next prime is 81635804323. The reversal of 81635804321 is 12340853618.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 12340853618 = 2 ⋅6170426809.

It is a cyclic number.

It is not a de Polignac number, because 81635804321 - 2²² = 81631610017 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81635804323) 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, 16073831 + ... + 16078908.

It is an arithmetic number, because the mean of its divisors is an integer number (20416989900).

Almost surely, 2^81635804321 is an apocalyptic number.

It is an amenable number.

81635804321 is a deficient number, since it is larger than the sum of its proper divisors (32155279).

81635804321 is a wasteful number, since it uses less digits than its factorization.

81635804321 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 32155278.

The product of its (nonzero) digits is 138240, while the sum is 41.

The spelling of 81635804321 in words is "eighty-one billion, six hundred thirty-five million, eight hundred four thousand, three hundred twenty-one".