666661561501 has 4 divisors (see below), whose sum is σ = 717943220092. Its totient is φ = 615379902912.

The previous prime is 666661561499. The next prime is 666661561523. The reversal of 666661561501 is 105165166666.

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 448036116025 + 218625445476 = 669355^2 + 467574^2 .

It is a cyclic number.

It is not a de Polignac number, because 666661561501 - 2¹ = 666661561499 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 (666661561301) 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, 25640829276 + ... + 25640829301.

It is an arithmetic number, because the mean of its divisors is an integer number (179485805023).

Almost surely, 2^666661561501 is an apocalyptic number.

It is an amenable number.

666661561501 is a deficient number, since it is larger than the sum of its proper divisors (51281658591).

666661561501 is a wasteful number, since it uses less digits than its factorization.

666661561501 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 51281658590.

The product of its (nonzero) digits is 1166400, while the sum is 49.

The spelling of 666661561501 in words is "six hundred sixty-six billion, six hundred sixty-one million, five hundred sixty-one thousand, five hundred one".