21375651821 has 2 divisors, whose sum is σ = 21375651822. Its totient is φ = 21375651820.

The previous prime is 21375651779. The next prime is 21375651823. The reversal of 21375651821 is 12815657312.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12273537796 + 9102114025 = 110786^2 + 95405^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21375651821 is a prime.

Together with 21375651823, 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 (21375651823) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10687825910 + 10687825911.

It is an arithmetic number, because the mean of its divisors is an integer number (10687825911).

Almost surely, 2^21375651821 is an apocalyptic number.

It is an amenable number.

21375651821 is a deficient number, since it is larger than the sum of its proper divisors (1).

21375651821 is an equidigital number, since it uses as much as digits as its factorization.

21375651821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 100800, while the sum is 41.

The spelling of 21375651821 in words is "twenty-one billion, three hundred seventy-five million, six hundred fifty-one thousand, eight hundred twenty-one".