21112009 has 2 divisors, whose sum is σ = 21112010. Its totient is φ = 21112008.

The previous prime is 21111991. The next prime is 21112019. The reversal of 21112009 is 90021112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15366400 + 5745609 = 3920^2 + 2397^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21112009 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21111983 and 21112001.

It is not a weakly prime, because it can be changed into another prime (21112019) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10556004 + 10556005.

It is an arithmetic number, because the mean of its divisors is an integer number (10556005).

Almost surely, 2^21112009 is an apocalyptic number.

It is an amenable number.

21112009 is a deficient number, since it is larger than the sum of its proper divisors (1).

21112009 is an equidigital number, since it uses as much as digits as its factorization.

21112009 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 36, while the sum is 16.

The square root of 21112009 is about 4594.7806258841. The cubic root of 21112009 is about 276.3820629391.

It can be divided in two parts, 2111200 and 9, that added together give a square (2111209 = 1453²).

The spelling of 21112009 in words is "twenty-one million, one hundred twelve thousand, nine".