21129985 has 16 divisors (see below), whose sum is σ = 27080064. Its totient is φ = 15789312.

The previous prime is 21129961. The next prime is 21129989. The reversal of 21129985 is 58992112.

It is a cyclic number.

It is not a de Polignac number, because 21129985 - 2¹⁵ = 21097217 is a prime.

It is a super-2 number, since 2×21129985² = 892952532200450, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21129989) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2809 + ... + 7081.

It is an arithmetic number, because the mean of its divisors is an integer number (1692504).

Almost surely, 2^21129985 is an apocalyptic number.

It is an amenable number.

21129985 is a deficient number, since it is larger than the sum of its proper divisors (5950079).

21129985 is a wasteful number, since it uses less digits than its factorization.

21129985 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4344.

The product of its digits is 12960, while the sum is 37.

The square root of 21129985 is about 4596.7363422324. The cubic root of 21129985 is about 276.4604833071.

The spelling of 21129985 in words is "twenty-one million, one hundred twenty-nine thousand, nine hundred eighty-five".