81661404521 has 8 divisors (see below), whose sum is σ = 87136900320. Its totient is φ = 76303661472.

The previous prime is 81661404509. The next prime is 81661404581. The reversal of 81661404521 is 12540416618.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 81661404521 - 2¹⁸ = 81661142377 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81661404581) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 29436755 + ... + 29439528.

It is an arithmetic number, because the mean of its divisors is an integer number (10892112540).

Almost surely, 2^81661404521 is an apocalyptic number.

It is an amenable number.

81661404521 is a deficient number, since it is larger than the sum of its proper divisors (5475495799).

81661404521 is a wasteful number, since it uses less digits than its factorization.

81661404521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 58876375.

The product of its (nonzero) digits is 46080, while the sum is 38.

The spelling of 81661404521 in words is "eighty-one billion, six hundred sixty-one million, four hundred four thousand, five hundred twenty-one".