66405721555 has 64 divisors (see below), whose sum is σ = 89077874688. Its totient is φ = 47266785280.

The previous prime is 66405721549. The next prime is 66405721583. The reversal of 66405721555 is 55512750466.

It is not a de Polignac number, because 66405721555 - 2²⁹ = 65868850643 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 98087877 + ... + 98088553.

It is an arithmetic number, because the mean of its divisors is an integer number (1391841792).

Almost surely, 2^66405721555 is an apocalyptic number.

66405721555 is a deficient number, since it is larger than the sum of its proper divisors (22672153133).

66405721555 is a wasteful number, since it uses less digits than its factorization.

66405721555 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1236.

The product of its (nonzero) digits is 1260000, while the sum is 46.

The spelling of 66405721555 in words is "sixty-six billion, four hundred five million, seven hundred twenty-one thousand, five hundred fifty-five".