81681773221 has 4 divisors (see below), whose sum is σ = 81682945344. Its totient is φ = 81680601100.

The previous prime is 81681773209. The next prime is 81681773269. The reversal of 81681773221 is 12237718618.

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.

It is a cyclic number.

It is not a de Polignac number, because 81681773221 - 2¹⁷ = 81681642149 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81681773291) 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, 474445 + ... + 623266.

It is an arithmetic number, because the mean of its divisors is an integer number (20420736336).

Almost surely, 2^81681773221 is an apocalyptic number.

It is an amenable number.

81681773221 is a deficient number, since it is larger than the sum of its proper divisors (1172123).

81681773221 is a wasteful number, since it uses less digits than its factorization.

81681773221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1172122.

The product of its digits is 225792, while the sum is 46.

The spelling of 81681773221 in words is "eighty-one billion, six hundred eighty-one million, seven hundred seventy-three thousand, two hundred twenty-one".