21210909 has 8 divisors (see below), whose sum is σ = 28561632. Its totient is φ = 14000400.

The previous prime is 21210907. The next prime is 21210929. The reversal of 21210909 is 90901212.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21210909 - 2¹ = 21210907 is a prime.

It is a super-3 number, since 3×21210909³ (a number of 23 digits) contains 333 as substring.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21210901) 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 in 7 ways as a sum of consecutive naturals, for example, 34699 + ... + 35304.

It is an arithmetic number, because the mean of its divisors is an integer number (3570204).

Almost surely, 2^21210909 is an apocalyptic number.

It is an amenable number.

21210909 is a deficient number, since it is larger than the sum of its proper divisors (7350723).

21210909 is a wasteful number, since it uses less digits than its factorization.

21210909 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 70107.

The product of its (nonzero) digits is 324, while the sum is 24.

The square root of 21210909 is about 4605.5302626299. The cubic root of 21210909 is about 276.8129648346.

The spelling of 21210909 in words is "twenty-one million, two hundred ten thousand, nine hundred nine".