21980217821 has 2 divisors, whose sum is σ = 21980217822. Its totient is φ = 21980217820.

The previous prime is 21980217803. The next prime is 21980217829. The reversal of 21980217821 is 12871208912.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13342560100 + 8637657721 = 115510^2 + 92939^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21980217821 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21980217829) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10990108910 + 10990108911.

It is an arithmetic number, because the mean of its divisors is an integer number (10990108911).

Almost surely, 2^21980217821 is an apocalyptic number.

It is an amenable number.

21980217821 is a deficient number, since it is larger than the sum of its proper divisors (1).

21980217821 is an equidigital number, since it uses as much as digits as its factorization.

21980217821 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 32256, while the sum is 41.

The spelling of 21980217821 in words is "twenty-one billion, nine hundred eighty million, two hundred seventeen thousand, eight hundred twenty-one".