21111111997 has 2 divisors, whose sum is σ = 21111111998. Its totient is φ = 21111111996.

The previous prime is 21111111971. The next prime is 21111112013. The reversal of 21111111997 is 79911111112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17169909156 + 3941202841 = 131034^2 + 62779^2 .

It is a cyclic number.

It is not a de Polignac number, because 21111111997 - 2³¹ = 18963628349 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21111111947) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10555555998 + 10555555999.

It is an arithmetic number, because the mean of its divisors is an integer number (10555555999).

Almost surely, 2^21111111997 is an apocalyptic number.

It is an amenable number.

21111111997 is a deficient number, since it is larger than the sum of its proper divisors (1).

21111111997 is an equidigital number, since it uses as much as digits as its factorization.

21111111997 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1134, while the sum is 34.

The spelling of 21111111997 in words is "twenty-one billion, one hundred eleven million, one hundred eleven thousand, nine hundred ninety-seven".