21712109 has 2 divisors, whose sum is σ = 21712110. Its totient is φ = 21712108.

The previous prime is 21712099. The next prime is 21712133. The reversal of 21712109 is 90121712.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17724100 + 3988009 = 4210^2 + 1997^2 .

It is a cyclic number.

It is not a de Polignac number, because 21712109 - 2⁸ = 21711853 is a prime.

It is a super-3 number, since 3×21712109³ (a number of 23 digits) contains 333 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21712169) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10856054 + 10856055.

It is an arithmetic number, because the mean of its divisors is an integer number (10856055).

Almost surely, 2^21712109 is an apocalyptic number.

It is an amenable number.

21712109 is a deficient number, since it is larger than the sum of its proper divisors (1).

21712109 is an equidigital number, since it uses as much as digits as its factorization.

21712109 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 252, while the sum is 23.

The square root of 21712109 is about 4659.6254141293. The cubic root of 21712109 is about 278.9763172388.

The spelling of 21712109 in words is "twenty-one million, seven hundred twelve thousand, one hundred nine".