21208818251 has 2 divisors, whose sum is σ = 21208818252. Its totient is φ = 21208818250.

The previous prime is 21208818247. The next prime is 21208818277. The reversal of 21208818251 is 15281880212.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21208818251 - 2² = 21208818247 is a prime.

It is not a weakly prime, because it can be changed into another prime (21208818151) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10604409125 + 10604409126.

It is an arithmetic number, because the mean of its divisors is an integer number (10604409126).

Almost surely, 2^21208818251 is an apocalyptic number.

21208818251 is a deficient number, since it is larger than the sum of its proper divisors (1).

21208818251 is an equidigital number, since it uses as much as digits as its factorization.

21208818251 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 20480, while the sum is 38.

The spelling of 21208818251 in words is "twenty-one billion, two hundred eight million, eight hundred eighteen thousand, two hundred fifty-one".