21630644921 has 2 divisors, whose sum is σ = 21630644922. Its totient is φ = 21630644920.

The previous prime is 21630644911. The next prime is 21630644923. The reversal of 21630644921 is 12944603612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19053661225 + 2576983696 = 138035^2 + 50764^2 .

It is a cyclic number.

It is not a de Polignac number, because 21630644921 - 2¹⁸ = 21630382777 is a prime.

It is a Sophie Germain prime.

Together with 21630644923, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (21630644923) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10815322460 + 10815322461.

It is an arithmetic number, because the mean of its divisors is an integer number (10815322461).

Almost surely, 2^21630644921 is an apocalyptic number.

It is an amenable number.

21630644921 is a deficient number, since it is larger than the sum of its proper divisors (1).

21630644921 is an equidigital number, since it uses as much as digits as its factorization.

21630644921 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 62208, while the sum is 38.

The spelling of 21630644921 in words is "twenty-one billion, six hundred thirty million, six hundred forty-four thousand, nine hundred twenty-one".