21011009 has 2 divisors, whose sum is σ = 21011010. Its totient is φ = 21011008.

The previous prime is 21010987. The next prime is 21011033. The reversal of 21011009 is 90011012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17247409 + 3763600 = 4153^2 + 1940^2 .

It is a cyclic number.

It is not a de Polignac number, because 21011009 - 2²⁴ = 4233793 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21010984 and 21011002.

It is not a weakly prime, because it can be changed into another prime (21011509) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10505504 + 10505505.

It is an arithmetic number, because the mean of its divisors is an integer number (10505505).

Almost surely, 2^21011009 is an apocalyptic number.

It is an amenable number.

21011009 is a deficient number, since it is larger than the sum of its proper divisors (1).

21011009 is an equidigital number, since it uses as much as digits as its factorization.

21011009 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 18, while the sum is 14.

The square root of 21011009 is about 4583.7767179478. The cubic root of 21011009 is about 275.9406203210.

The spelling of 21011009 in words is "twenty-one million, eleven thousand, nine".