21031009 has 2 divisors, whose sum is σ = 21031010. Its totient is φ = 21031008.

The previous prime is 21030979. The next prime is 21031019. The reversal of 21031009 is 90013012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18318400 + 2712609 = 4280^2 + 1647^2 .

It is a cyclic number.

It is not a de Polignac number, because 21031009 - 2⁷ = 21030881 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21030983 and 21031001.

It is not a weakly prime, because it can be changed into another prime (21031019) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10515504 + 10515505.

It is an arithmetic number, because the mean of its divisors is an integer number (10515505).

Almost surely, 2^21031009 is an apocalyptic number.

It is an amenable number.

21031009 is a deficient number, since it is larger than the sum of its proper divisors (1).

21031009 is an equidigital number, since it uses as much as digits as its factorization.

21031009 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 54, while the sum is 16.

The square root of 21031009 is about 4585.9578061731. The cubic root of 21031009 is about 276.0281468529.

The spelling of 21031009 in words is "twenty-one million, thirty-one thousand, nine".