21259166809 has 2 divisors, whose sum is σ = 21259166810. Its totient is φ = 21259166808.

The previous prime is 21259166771. The next prime is 21259166813. The reversal of 21259166809 is 90866195212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21187713600 + 71453209 = 145560^2 + 8453^2 .

It is a cyclic number.

It is not a de Polignac number, because 21259166809 - 2¹¹ = 21259164761 is a prime.

It is not a weakly prime, because it can be changed into another prime (21259166879) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10629583404 + 10629583405.

It is an arithmetic number, because the mean of its divisors is an integer number (10629583405).

Almost surely, 2^21259166809 is an apocalyptic number.

It is an amenable number.

21259166809 is a deficient number, since it is larger than the sum of its proper divisors (1).

21259166809 is an equidigital number, since it uses as much as digits as its factorization.

21259166809 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 466560, while the sum is 49.

The spelling of 21259166809 in words is "twenty-one billion, two hundred fifty-nine million, one hundred sixty-six thousand, eight hundred nine".