66506505656561 has 4 divisors (see below), whose sum is σ = 68303978782452. Its totient is φ = 64709032530672.

The previous prime is 66506505656543. The next prime is 66506505656573. The reversal of 66506505656561 is 16565650560566.

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 47155084705936 + 19351420950625 = 6866956^2 + 4399025^2 .

It is a cyclic number.

It is not a de Polignac number, because 66506505656561 - 2¹⁴ = 66506505640177 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 66506505656494 and 66506505656503.

It is not an unprimeable number, because it can be changed into a prime (66506505656861) 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, 898736562890 + ... + 898736562963.

It is an arithmetic number, because the mean of its divisors is an integer number (17075994695613).

Almost surely, 2^{66506505656561} is an apocalyptic number.

It is an amenable number.

66506505656561 is a deficient number, since it is larger than the sum of its proper divisors (1797473125891).

66506505656561 is a wasteful number, since it uses less digits than its factorization.

66506505656561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1797473125890.

The product of its (nonzero) digits is 145800000, while the sum is 62.

The spelling of 66506505656561 in words is "sixty-six trillion, five hundred six billion, five hundred five million, six hundred fifty-six thousand, five hundred sixty-one".