81209456641 has 4 divisors (see below), whose sum is σ = 81573624832. Its totient is φ = 80845288452.

The previous prime is 81209456617. The next prime is 81209456663. The reversal of 81209456641 is 14665490218.

It is a happy number.

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 81209456641 - 2⁵ = 81209456609 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 81209456591 and 81209456600.

It is not an unprimeable number, because it can be changed into a prime (81209451641) 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, 182083761 + ... + 182084206.

It is an arithmetic number, because the mean of its divisors is an integer number (20393406208).

Almost surely, 2^81209456641 is an apocalyptic number.

It is an amenable number.

81209456641 is a deficient number, since it is larger than the sum of its proper divisors (364168191).

81209456641 is a wasteful number, since it uses less digits than its factorization.

81209456641 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 364168190.

The product of its (nonzero) digits is 414720, while the sum is 46.

The spelling of 81209456641 in words is "eighty-one billion, two hundred nine million, four hundred fifty-six thousand, six hundred forty-one".