21001167809 has 2 divisors, whose sum is σ = 21001167810. Its totient is φ = 21001167808.

The previous prime is 21001167791. The next prime is 21001167841. The reversal of 21001167809 is 90876110012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20708073409 + 293094400 = 143903^2 + 17120^2 .

It is a cyclic number.

It is not a de Polignac number, because 21001167809 - 2¹² = 21001163713 is a prime.

It is not a weakly prime, because it can be changed into another prime (21001167409) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10500583904 + 10500583905.

It is an arithmetic number, because the mean of its divisors is an integer number (10500583905).

Almost surely, 2^21001167809 is an apocalyptic number.

It is an amenable number.

21001167809 is a deficient number, since it is larger than the sum of its proper divisors (1).

21001167809 is an equidigital number, since it uses as much as digits as its factorization.

21001167809 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 6048, while the sum is 35.

The spelling of 21001167809 in words is "twenty-one billion, one million, one hundred sixty-seven thousand, eight hundred nine".