681355561 has 4 divisors (see below), whose sum is σ = 717216400. Its totient is φ = 645494724.

The previous prime is 681355559. The next prime is 681355567. The reversal of 681355561 is 165553186.

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, and also an emirpimes, since its reverse is a distinct semiprime: 165553186 = 2 ⋅82776593.

It is a cyclic number.

It is not a de Polignac number, because 681355561 - 2¹ = 681355559 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (681355567) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 17930391 + ... + 17930428.

It is an arithmetic number, because the mean of its divisors is an integer number (179304100).

Almost surely, 2^681355561 is an apocalyptic number.

It is an amenable number.

681355561 is a deficient number, since it is larger than the sum of its proper divisors (35860839).

681355561 is a wasteful number, since it uses less digits than its factorization.

681355561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 35860838.

The product of its digits is 108000, while the sum is 40.

The square root of 681355561 is about 26102.7883759571. The cubic root of 681355561 is about 879.9498770522.

The spelling of 681355561 in words is "six hundred eighty-one million, three hundred fifty-five thousand, five hundred sixty-one".