16561999997 has 2 divisors, whose sum is σ = 16561999998. Its totient is φ = 16561999996.

The previous prime is 16561999939. The next prime is 16562000033. The reversal of 16561999997 is 79999916561.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12909731641 + 3652268356 = 113621^2 + 60434^2 .

It is an emirp because it is prime and its reverse (79999916561) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 16561999997 - 2¹⁸ = 16561737853 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 16561999997.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (16561999907) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8280999998 + 8280999999.

It is an arithmetic number, because the mean of its divisors is an integer number (8280999999).

Almost surely, 2^16561999997 is an apocalyptic number.

It is an amenable number.

16561999997 is a deficient number, since it is larger than the sum of its proper divisors (1).

16561999997 is an equidigital number, since it uses as much as digits as its factorization.

16561999997 is an evil number, because the sum of its binary digits is even.

The product of its digits is 74401740, while the sum is 71.

The spelling of 16561999997 in words is "sixteen billion, five hundred sixty-one million, nine hundred ninety-nine thousand, nine hundred ninety-seven".