21001001009 has 2 divisors, whose sum is σ = 21001001010. Its totient is φ = 21001001008.

The previous prime is 21001000991. The next prime is 21001001041. The reversal of 21001001009 is 90010010012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13899231025 + 7101769984 = 117895^2 + 84272^2 .

It is a cyclic number.

It is not a de Polignac number, because 21001001009 - 2²⁰ = 20999952433 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21001000984 and 21001001002.

It is not a weakly prime, because it can be changed into another prime (21001001209) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10500500504 + 10500500505.

It is an arithmetic number, because the mean of its divisors is an integer number (10500500505).

Almost surely, 2^21001001009 is an apocalyptic number.

It is an amenable number.

21001001009 is a deficient number, since it is larger than the sum of its proper divisors (1).

21001001009 is an equidigital number, since it uses as much as digits as its factorization.

21001001009 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 spelling of 21001001009 in words is "twenty-one billion, one million, one thousand, nine".