81665057156651 has 4 divisors (see below), whose sum is σ = 81665098523904. Its totient is φ = 81665015789400.

The previous prime is 81665057156647. The next prime is 81665057156653. The reversal of 81665057156651 is 15665175056618.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 81665057156651 - 2² = 81665057156647 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81665057156653) 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, 17565740 + ... + 21722921.

It is an arithmetic number, because the mean of its divisors is an integer number (20416274630976).

Almost surely, 2^{81665057156651} is an apocalyptic number.

81665057156651 is a deficient number, since it is larger than the sum of its proper divisors (41367253).

81665057156651 is a wasteful number, since it uses less digits than its factorization.

81665057156651 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 41367252.

The product of its (nonzero) digits is 45360000, while the sum is 62.

The spelling of 81665057156651 in words is "eighty-one trillion, six hundred sixty-five billion, fifty-seven million, one hundred fifty-six thousand, six hundred fifty-one".