6406521165661 has 4 divisors (see below), whose sum is σ = 6685065564192. Its totient is φ = 6127976767132.

The previous prime is 6406521165647. The next prime is 6406521165719. The reversal of 6406521165661 is 1665611256046.

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 not a de Polignac number, because 6406521165661 - 2³¹ = 6404373682013 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 (6406521165461) 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, 139272199231 + ... + 139272199276.

It is an arithmetic number, because the mean of its divisors is an integer number (1671266391048).

Almost surely, 2^{6406521165661} is an apocalyptic number.

It is an amenable number.

6406521165661 is a deficient number, since it is larger than the sum of its proper divisors (278544398531).

6406521165661 is a wasteful number, since it uses less digits than its factorization.

6406521165661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 278544398530.

The product of its (nonzero) digits is 1555200, while the sum is 49.

The spelling of 6406521165661 in words is "six trillion, four hundred six billion, five hundred twenty-one million, one hundred sixty-five thousand, six hundred sixty-one".