21387703817 has 2 divisors, whose sum is σ = 21387703818. Its totient is φ = 21387703816.

The previous prime is 21387703807. The next prime is 21387703853. The reversal of 21387703817 is 71830778312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13095598096 + 8292105721 = 114436^2 + 91061^2 .

It is a cyclic number.

It is not a de Polignac number, because 21387703817 - 2⁴ = 21387703801 is a prime.

It is not a weakly prime, because it can be changed into another prime (21387703807) 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, 10693851908 + 10693851909.

It is an arithmetic number, because the mean of its divisors is an integer number (10693851909).

Almost surely, 2^21387703817 is an apocalyptic number.

It is an amenable number.

21387703817 is a deficient number, since it is larger than the sum of its proper divisors (1).

21387703817 is an equidigital number, since it uses as much as digits as its factorization.

21387703817 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 395136, while the sum is 47.

The spelling of 21387703817 in words is "twenty-one billion, three hundred eighty-seven million, seven hundred three thousand, eight hundred seventeen".