6561999 has 16 divisors (see below), whose sum is σ = 9930240. Its totient is φ = 4280760.

The previous prime is 6561991. The next prime is 6562001. The reversal of 6561999 is 9991656.

It is not a de Polignac number, because 6561999 - 2³ = 6561991 is a prime.

6561999 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (6561991) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1317 + ... + 3854.

It is an arithmetic number, because the mean of its divisors is an integer number (620640).

Almost surely, 2^6561999 is an apocalyptic number.

6561999 is a deficient number, since it is larger than the sum of its proper divisors (3368241).

6561999 is a wasteful number, since it uses less digits than its factorization.

6561999 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5227 (or 5221 counting only the distinct ones).

The product of its digits is 131220, while the sum is 45.

The square root of 6561999 is about 2561.6399044362. The cubic root of 6561999 is about 187.2170452099.

The spelling of 6561999 in words is "six million, five hundred sixty-one thousand, nine hundred ninety-nine".