6561981 has 12 divisors (see below), whose sum is σ = 9518652. Its totient is φ = 4356096.

The previous prime is 6561943. The next prime is 6561991. The reversal of 6561981 is 1891656.

6561981 is a `hidden beast` number, since 6 + 561 + 98 + 1 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 3481956 + 3080025 = 1866^2 + 1755^2 .

It is not a de Polignac number, because 6561981 - 2¹⁸ = 6299837 is a prime.

It is a super-2 number, since 2×6561981² = 86119189288722, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (6561911) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 895 + ... + 3731.

It is an arithmetic number, because the mean of its divisors is an integer number (793221).

Almost surely, 2^6561981 is an apocalyptic number.

It is an amenable number.

6561981 is a deficient number, since it is larger than the sum of its proper divisors (2956671).

6561981 is a wasteful number, since it uses less digits than its factorization.

6561981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3100 (or 3097 counting only the distinct ones).

The product of its digits is 12960, while the sum is 36.

The square root of 6561981 is about 2561.6363910594. The cubic root of 6561981 is about 187.2168740268.

The spelling of 6561981 in words is "six million, five hundred sixty-one thousand, nine hundred eighty-one".