16581329561 has 2 divisors, whose sum is σ = 16581329562. Its totient is φ = 16581329560.

The previous prime is 16581329551. The next prime is 16581329581. The reversal of 16581329561 is 16592318561.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16578107536 + 3222025 = 128756^2 + 1795^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-16581329561 is a prime.

It is not a weakly prime, because it can be changed into another prime (16581329551) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8290664780 + 8290664781.

It is an arithmetic number, because the mean of its divisors is an integer number (8290664781).

Almost surely, 2^16581329561 is an apocalyptic number.

It is an amenable number.

16581329561 is a deficient number, since it is larger than the sum of its proper divisors (1).

16581329561 is an equidigital number, since it uses as much as digits as its factorization.

16581329561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 388800, while the sum is 47.

The spelling of 16581329561 in words is "sixteen billion, five hundred eighty-one million, three hundred twenty-nine thousand, five hundred sixty-one".