66623521661 has 4 divisors (see below), whose sum is σ = 66914454300. Its totient is φ = 66332589024.

The previous prime is 66623521583. The next prime is 66623521667. The reversal of 66623521661 is 16612532666.

66623521661 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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 35083537636 + 31539984025 = 187306^2 + 177595^2 .

It is a cyclic number.

It is not a de Polignac number, because 66623521661 - 2³⁴ = 49443652477 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66623521667) 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, 145465976 + ... + 145466433.

It is an arithmetic number, because the mean of its divisors is an integer number (16728613575).

Almost surely, 2^66623521661 is an apocalyptic number.

It is an amenable number.

66623521661 is a deficient number, since it is larger than the sum of its proper divisors (290932639).

66623521661 is a wasteful number, since it uses less digits than its factorization.

66623521661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 290932638.

The product of its digits is 466560, while the sum is 44.

The spelling of 66623521661 in words is "sixty-six billion, six hundred twenty-three million, five hundred twenty-one thousand, six hundred sixty-one".