21209985 has 32 divisors (see below), whose sum is σ = 39696000. Its totient is φ = 10715328.

The previous prime is 21209963. The next prime is 21210011. The reversal of 21209985 is 58990212.

It is not a de Polignac number, because 21209985 - 2¹⁰ = 21208961 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 1570 + ... + 6699.

It is an arithmetic number, because the mean of its divisors is an integer number (1240500).

Almost surely, 2^21209985 is an apocalyptic number.

It is an amenable number.

21209985 is a deficient number, since it is larger than the sum of its proper divisors (18486015).

21209985 is a wasteful number, since it uses less digits than its factorization.

21209985 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8302 (or 8296 counting only the distinct ones).

The product of its (nonzero) digits is 12960, while the sum is 36.

The square root of 21209985 is about 4605.4299473556. The cubic root of 21209985 is about 276.8089452222.

The spelling of 21209985 in words is "twenty-one million, two hundred nine thousand, nine hundred eighty-five".