21210999917 has 2 divisors, whose sum is σ = 21210999918. Its totient is φ = 21210999916.

The previous prime is 21210999911. The next prime is 21210999973. The reversal of 21210999917 is 71999901212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 10672129636 + 10538870281 = 103306^2 + 102659^2 .

It is a cyclic number.

It is not a de Polignac number, because 21210999917 - 2⁶ = 21210999853 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21210999911) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10605499958 + 10605499959.

It is an arithmetic number, because the mean of its divisors is an integer number (10605499959).

Almost surely, 2^21210999917 is an apocalyptic number.

It is an amenable number.

21210999917 is a deficient number, since it is larger than the sum of its proper divisors (1).

21210999917 is an equidigital number, since it uses as much as digits as its factorization.

21210999917 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 183708, while the sum is 50.

The spelling of 21210999917 in words is "twenty-one billion, two hundred ten million, nine hundred ninety-nine thousand, nine hundred seventeen".