51666420665 has 4 divisors (see below), whose sum is σ = 61999704804. Its totient is φ = 41333136528.

The previous prime is 51666420647. The next prime is 51666420667. The reversal of 51666420665 is 56602466615.

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 13624258729 + 38042161936 = 116723^2 + 195044^2 .

It is a cyclic number.

It is not a de Polignac number, because 51666420665 - 2⁶ = 51666420601 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (51666420667) 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, 5166642062 + ... + 5166642071.

It is an arithmetic number, because the mean of its divisors is an integer number (15499926201).

Almost surely, 2^51666420665 is an apocalyptic number.

It is an amenable number.

51666420665 is a deficient number, since it is larger than the sum of its proper divisors (10333284139).

51666420665 is a wasteful number, since it uses less digits than its factorization.

51666420665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10333284138.

The product of its (nonzero) digits is 1555200, while the sum is 47.

The spelling of 51666420665 in words is "fifty-one billion, six hundred sixty-six million, four hundred twenty thousand, six hundred sixty-five".