21810109 has 2 divisors, whose sum is σ = 21810110. Its totient is φ = 21810108.

The previous prime is 21810079. The next prime is 21810121. The reversal of 21810109 is 90101812.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21252100 + 558009 = 4610^2 + 747^2 .

It is a cyclic number.

It is not a de Polignac number, because 21810109 - 2⁵ = 21810077 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a self number, because there is not a number n which added to its sum of digits gives 21810109.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21810169) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10905054 + 10905055.

It is an arithmetic number, because the mean of its divisors is an integer number (10905055).

Almost surely, 2^21810109 is an apocalyptic number.

It is an amenable number.

21810109 is a deficient number, since it is larger than the sum of its proper divisors (1).

21810109 is an equidigital number, since it uses as much as digits as its factorization.

21810109 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 144, while the sum is 22.

The square root of 21810109 is about 4670.1294414609. The cubic root of 21810109 is about 279.3954174496.

It can be divided in two parts, 21810 and 109, that multiplied together give a triangular number (2377290 = T₂₁₈₀).

The spelling of 21810109 in words is "twenty-one million, eight hundred ten thousand, one hundred nine".