21609109 has 2 divisors, whose sum is σ = 21609110. Its totient is φ = 21609108.

The previous prime is 21609101. The next prime is 21609131. The reversal of 21609109 is 90190612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18037009 + 3572100 = 4247^2 + 1890^2 .

It is a cyclic number.

It is not a de Polignac number, because 21609109 - 2³ = 21609101 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21609101) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10804554 + 10804555.

It is an arithmetic number, because the mean of its divisors is an integer number (10804555).

Almost surely, 2^21609109 is an apocalyptic number.

It is an amenable number.

21609109 is a deficient number, since it is larger than the sum of its proper divisors (1).

21609109 is an equidigital number, since it uses as much as digits as its factorization.

21609109 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 972, while the sum is 28.

The square root of 21609109 is about 4648.5598845234. The cubic root of 21609109 is about 278.5344728785.

The spelling of 21609109 in words is "twenty-one million, six hundred nine thousand, one hundred nine".