21006623021 has 2 divisors, whose sum is σ = 21006623022. Its totient is φ = 21006623020.

The previous prime is 21006622997. The next prime is 21006623023. The reversal of 21006623021 is 12032660012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19827456100 + 1179166921 = 140810^2 + 34339^2 .

It is a cyclic number.

It is not a de Polignac number, because 21006623021 - 2⁶ = 21006622957 is a prime.

Together with 21006623023, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21006623023) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10503311510 + 10503311511.

It is an arithmetic number, because the mean of its divisors is an integer number (10503311511).

Almost surely, 2^21006623021 is an apocalyptic number.

It is an amenable number.

21006623021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21006623021 is an equidigital number, since it uses as much as digits as its factorization.

21006623021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 864, while the sum is 23.

The spelling of 21006623021 in words is "twenty-one billion, six million, six hundred twenty-three thousand, twenty-one".