21012002009 has 2 divisors, whose sum is σ = 21012002010. Its totient is φ = 21012002008.

The previous prime is 21012001991. The next prime is 21012002021. The reversal of 21012002009 is 90020021012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14430736384 + 6581265625 = 120128^2 + 81125^2 .

It is a cyclic number.

It is not a de Polignac number, because 21012002009 - 2⁸ = 21012001753 is a prime.

It is not a weakly prime, because it can be changed into another prime (21012002509) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10506001004 + 10506001005.

It is an arithmetic number, because the mean of its divisors is an integer number (10506001005).

Almost surely, 2^21012002009 is an apocalyptic number.

It is an amenable number.

21012002009 is a deficient number, since it is larger than the sum of its proper divisors (1).

21012002009 is an equidigital number, since it uses as much as digits as its factorization.

21012002009 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 72, while the sum is 17.

The spelling of 21012002009 in words is "twenty-one billion, twelve million, two thousand, nine".