6561516666566 has 4 divisors (see below), whose sum is σ = 9842274999852. Its totient is φ = 3280758333282.

The previous prime is 6561516666563. The next prime is 6561516666577. The reversal of 6561516666566 is 6656666151656.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (6561516666563) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (29) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1640379166640 + ... + 1640379166643.

It is an arithmetic number, because the mean of its divisors is an integer number (2460568749963).

Almost surely, 2^{6561516666566} is an apocalyptic number.

6561516666566 is a deficient number, since it is larger than the sum of its proper divisors (3280758333286).

6561516666566 is a wasteful number, since it uses less digits than its factorization.

6561516666566 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3280758333285.

The product of its digits is 209952000, while the sum is 65.

The spelling of 6561516666566 in words is "six trillion, five hundred sixty-one billion, five hundred sixteen million, six hundred sixty-six thousand, five hundred sixty-six".