21210309821 has 2 divisors, whose sum is σ = 21210309822. Its totient is φ = 21210309820.

The previous prime is 21210309787. The next prime is 21210309847. The reversal of 21210309821 is 12890301212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16530244900 + 4680064921 = 128570^2 + 68411^2 .

It is a cyclic number.

It is not a de Polignac number, because 21210309821 - 2²⁶ = 21143200957 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21210309521) 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, 10605154910 + 10605154911.

It is an arithmetic number, because the mean of its divisors is an integer number (10605154911).

Almost surely, 2^21210309821 is an apocalyptic number.

It is an amenable number.

21210309821 is a deficient number, since it is larger than the sum of its proper divisors (1).

21210309821 is an equidigital number, since it uses as much as digits as its factorization.

21210309821 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1728, while the sum is 29.

The spelling of 21210309821 in words is "twenty-one billion, two hundred ten million, three hundred nine thousand, eight hundred twenty-one".