20210121209 has 2 divisors, whose sum is σ = 20210121210. Its totient is φ = 20210121208.

The previous prime is 20210121089. The next prime is 20210121227. The reversal of 20210121209 is 90212101202.

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., 12453444025 + 7756677184 = 111595^2 + 88072^2 .

It is a cyclic number.

It is not a de Polignac number, because 20210121209 - 2¹⁶ = 20210055673 is a prime.

It is not a weakly prime, because it can be changed into another prime (20210121289) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10105060604 + 10105060605.

It is an arithmetic number, because the mean of its divisors is an integer number (10105060605).

Almost surely, 2^20210121209 is an apocalyptic number.

It is an amenable number.

20210121209 is a deficient number, since it is larger than the sum of its proper divisors (1).

20210121209 is an equidigital number, since it uses as much as digits as its factorization.

20210121209 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 144, while the sum is 20.

The spelling of 20210121209 in words is "twenty billion, two hundred ten million, one hundred twenty-one thousand, two hundred nine".