6561665520 has 40 divisors (see below), whose sum is σ = 20341163856. Its totient is φ = 1749777408.

The previous prime is 6561665519. The next prime is 6561665549. The reversal of 6561665520 is 255661656.

It is a tau number, because it is divible by the number of its divisors (40).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 13669897 + ... + 13670376.

Almost surely, 2^6561665520 is an apocalyptic number.

6561665520 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

It is an amenable number.

6561665520 is an abundant number, since it is smaller than the sum of its proper divisors (13779498336).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

6561665520 is a wasteful number, since it uses less digits than its factorization.

6561665520 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27340289 (or 27340283 counting only the distinct ones).

The product of its (nonzero) digits is 324000, while the sum is 42.

The square root of 6561665520 is about 81004.1080439752. The cubic root of 6561665520 is about 1872.1387370696.

The spelling of 6561665520 in words is "six billion, five hundred sixty-one million, six hundred sixty-five thousand, five hundred twenty".