6561640 has 32 divisors (see below), whose sum is σ = 15127560. Its totient is φ = 2560000.

The previous prime is 6561637. The next prime is 6561649. The reversal of 6561640 is 461656.

It can be written as a sum of positive squares in 4 ways, for example, as 1695204 + 4866436 = 1302^2 + 2206^2 .

It is a junction number, because it is equal to n+sod(n) for n = 6561599 and 6561608.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (6561649) 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 7 ways as a sum of consecutive naturals, for example, 361 + ... + 3640.

Almost surely, 2^6561640 is an apocalyptic number.

It is an amenable number.

6561640 is an abundant number, since it is smaller than the sum of its proper divisors (8565920).

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

6561640 is a wasteful number, since it uses less digits than its factorization.

6561640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4053 (or 4049 counting only the distinct ones).

The product of its (nonzero) digits is 4320, while the sum is 28.

The square root of 6561640 is about 2561.5698311777. The cubic root of 6561640 is about 187.2136309991.

It can be divided in two parts, 65616 and 40, that added together give a palindrome (65656).

The spelling of 6561640 in words is "six million, five hundred sixty-one thousand, six hundred forty".