66505561501 has 4 divisors (see below), whose sum is σ = 70417653372. Its totient is φ = 62593469632.

The previous prime is 66505561477. The next prime is 66505561517. The reversal of 66505561501 is 10516550566.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 10516550566 = 2 ⋅5258275283.

It can be written as a sum of positive squares in 2 ways, for example, as 54721373476 + 11784188025 = 233926^2 + 108555^2 .

It is a cyclic number.

It is not a de Polignac number, because 66505561501 - 2⁵ = 66505561469 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 (66535561501) 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, 1956045910 + ... + 1956045943.

It is an arithmetic number, because the mean of its divisors is an integer number (17604413343).

Almost surely, 2^66505561501 is an apocalyptic number.

It is an amenable number.

66505561501 is a deficient number, since it is larger than the sum of its proper divisors (3912091871).

66505561501 is a wasteful number, since it uses less digits than its factorization.

66505561501 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3912091870.

The product of its (nonzero) digits is 135000, while the sum is 40.

The spelling of 66505561501 in words is "sixty-six billion, five hundred five million, five hundred sixty-one thousand, five hundred one".