6661215661 has 4 divisors (see below), whose sum is σ = 6705329824. Its totient is φ = 6617101500.

The previous prime is 6661215653. The next prime is 6661215761. The reversal of 6661215661 is 1665121666.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 6661215661 - 2³ = 6661215653 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 (6661215161) 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, 22056855 + ... + 22057156.

It is an arithmetic number, because the mean of its divisors is an integer number (1676332456).

Almost surely, 2^6661215661 is an apocalyptic number.

It is an amenable number.

6661215661 is a deficient number, since it is larger than the sum of its proper divisors (44114163).

6661215661 is a wasteful number, since it uses less digits than its factorization.

6661215661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 44114162.

The product of its digits is 77760, while the sum is 40.

The square root of 6661215661 is about 81616.2708104211. The cubic root of 6661215661 is about 1881.5589586187.

The spelling of 6661215661 in words is "six billion, six hundred sixty-one million, two hundred fifteen thousand, six hundred sixty-one".