6405216661 has 4 divisors (see below), whose sum is σ = 6554175232. Its totient is φ = 6256258092.

The previous prime is 6405216641. The next prime is 6405216691. The reversal of 6405216661 is 1666125046.

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 6405216661 - 2¹⁵ = 6405183893 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 6405216661.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (6405216641) 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, 74479221 + ... + 74479306.

It is an arithmetic number, because the mean of its divisors is an integer number (1638543808).

Almost surely, 2^6405216661 is an apocalyptic number.

It is an amenable number.

6405216661 is a deficient number, since it is larger than the sum of its proper divisors (148958571).

6405216661 is a wasteful number, since it uses less digits than its factorization.

6405216661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 148958570.

The product of its (nonzero) digits is 51840, while the sum is 37.

The square root of 6405216661 is about 80032.5974900228. The cubic root of 6405216661 is about 1857.1398463527.

The spelling of 6405216661 in words is "six billion, four hundred five million, two hundred sixteen thousand, six hundred sixty-one".