81021907685 has 4 divisors (see below), whose sum is σ = 97226289228. Its totient is φ = 64817526144.

The previous prime is 81021907663. The next prime is 81021907691. The reversal of 81021907685 is 58670912018.

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 22241844769 + 58780062916 = 149137^2 + 242446^2 .

It is a cyclic number.

It is not a de Polignac number, because 81021907685 - 2⁶ = 81021907621 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8102190764 + ... + 8102190773.

It is an arithmetic number, because the mean of its divisors is an integer number (24306572307).

Almost surely, 2^81021907685 is an apocalyptic number.

It is an amenable number.

81021907685 is a deficient number, since it is larger than the sum of its proper divisors (16204381543).

81021907685 is a wasteful number, since it uses less digits than its factorization.

81021907685 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16204381542.

The product of its (nonzero) digits is 241920, while the sum is 47.

The spelling of 81021907685 in words is "eighty-one billion, twenty-one million, nine hundred seven thousand, six hundred eighty-five".