21043212109 has 2 divisors, whose sum is σ = 21043212110. Its totient is φ = 21043212108.

The previous prime is 21043212103. The next prime is 21043212137. The reversal of 21043212109 is 90121234012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19529224009 + 1513988100 = 139747^2 + 38910^2 .

It is a cyclic number.

It is not a de Polignac number, because 21043212109 - 2⁵ = 21043212077 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21043212103) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10521606054 + 10521606055.

It is an arithmetic number, because the mean of its divisors is an integer number (10521606055).

Almost surely, 2^21043212109 is an apocalyptic number.

It is an amenable number.

21043212109 is a deficient number, since it is larger than the sum of its proper divisors (1).

21043212109 is an equidigital number, since it uses as much as digits as its factorization.

21043212109 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 864, while the sum is 25.

The spelling of 21043212109 in words is "twenty-one billion, forty-three million, two hundred twelve thousand, one hundred nine".