16581878821 has 2 divisors, whose sum is σ = 16581878822. Its totient is φ = 16581878820.

The previous prime is 16581878813. The next prime is 16581878837. The reversal of 16581878821 is 12887818561.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13991577796 + 2590301025 = 118286^2 + 50895^2 .

It is a cyclic number.

It is not a de Polignac number, because 16581878821 - 2³ = 16581878813 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (16581878881) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8290939410 + 8290939411.

It is an arithmetic number, because the mean of its divisors is an integer number (8290939411).

Almost surely, 2^16581878821 is an apocalyptic number.

It is an amenable number.

16581878821 is a deficient number, since it is larger than the sum of its proper divisors (1).

16581878821 is an equidigital number, since it uses as much as digits as its factorization.

16581878821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1720320, while the sum is 55.

The spelling of 16581878821 in words is "sixteen billion, five hundred eighty-one million, eight hundred seventy-eight thousand, eight hundred twenty-one".