6561234781 has 4 divisors (see below), whose sum is σ = 6572044672. Its totient is φ = 6550424892.

The previous prime is 6561234769. The next prime is 6561234791. The reversal of 6561234781 is 1874321656.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 6561234781 - 2¹⁹ = 6560710493 is a prime.

It is a super-2 number, since 2×6561234781² = 86099603702808235922, which contains 22 as substring.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (6561234751) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5404035 + ... + 5405248.

It is an arithmetic number, because the mean of its divisors is an integer number (1643011168).

Almost surely, 2^6561234781 is an apocalyptic number.

It is an amenable number.

6561234781 is a deficient number, since it is larger than the sum of its proper divisors (10809891).

6561234781 is a wasteful number, since it uses less digits than its factorization.

6561234781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10809890.

The product of its digits is 241920, while the sum is 43.

The square root of 6561234781 is about 81001.4492524671. The cubic root of 6561234781 is about 1872.0977708032.

The spelling of 6561234781 in words is "six billion, five hundred sixty-one million, two hundred thirty-four thousand, seven hundred eighty-one".