21406109 has 2 divisors, whose sum is σ = 21406110. Its totient is φ = 21406108.

The previous prime is 21406087. The next prime is 21406153. The reversal of 21406109 is 90160412.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 10824100 + 10582009 = 3290^2 + 3253^2 .

It is a cyclic number.

It is not a de Polignac number, because 21406109 - 2¹² = 21402013 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21406199) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10703054 + 10703055.

It is an arithmetic number, because the mean of its divisors is an integer number (10703055).

Almost surely, 2^21406109 is an apocalyptic number.

It is an amenable number.

21406109 is a deficient number, since it is larger than the sum of its proper divisors (1).

21406109 is an equidigital number, since it uses as much as digits as its factorization.

21406109 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 432, while the sum is 23.

The square root of 21406109 is about 4626.6736431263. The cubic root of 21406109 is about 277.6595257316.

The spelling of 21406109 in words is "twenty-one million, four hundred six thousand, one hundred nine".