6561602215666 has 4 divisors (see below), whose sum is σ = 9842403323502. Its totient is φ = 3280801107832.

The previous prime is 6561602215543. The next prime is 6561602215681. The reversal of 6561602215666 is 6665122061656.

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

It can be written as a sum of positive squares in only one way, i.e., 5445665624025 + 1115936591641 = 2333595^2 + 1056379^2 .

It is an unprimeable number.

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, 1640400553915 + ... + 1640400553918.

Almost surely, 2^{6561602215666} is an apocalyptic number.

6561602215666 is a deficient number, since it is larger than the sum of its proper divisors (3280801107836).

6561602215666 is a wasteful number, since it uses less digits than its factorization.

6561602215666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3280801107835.

The product of its (nonzero) digits is 4665600, while the sum is 52.

The spelling of 6561602215666 in words is "six trillion, five hundred sixty-one billion, six hundred two million, two hundred fifteen thousand, six hundred sixty-six".