6561555 has 128 divisors (see below), whose sum is σ = 15482880. Its totient is φ = 2280960.

The previous prime is 6561551. The next prime is 6561557. The reversal of 6561555 is 5551656.

It is not a de Polignac number, because 6561555 - 2² = 6561551 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (33).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (6561551) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 127 ways as a sum of consecutive naturals, for example, 285274 + ... + 285296.

It is an arithmetic number, because the mean of its divisors is an integer number (120960).

Almost surely, 2^6561555 is an apocalyptic number.

6561555 is a gapful number since it is divisible by the number (65) formed by its first and last digit.

6561555 is an abundant number, since it is smaller than the sum of its proper divisors (8921325).

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

6561555 is a wasteful number, since it uses less digits than its factorization.

6561555 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 81.

The product of its digits is 22500, while the sum is 33.

The square root of 6561555 is about 2561.5532397356. The cubic root of 6561555 is about 187.2128226022.

It can be divided in two parts, 656 and 1555, that added together give a triangular number (2211 = T₆₆).

The spelling of 6561555 in words is "six million, five hundred sixty-one thousand, five hundred fifty-five".