21172085 has 16 divisors (see below), whose sum is σ = 27820800. Its totient is φ = 15339840.

The previous prime is 21172057. The next prime is 21172087. The reversal of 21172085 is 58027112.

It is not a de Polignac number, because 21172085 - 2¹² = 21167989 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21172087) 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 15 ways as a sum of consecutive naturals, for example, 18644 + ... + 19746.

It is an arithmetic number, because the mean of its divisors is an integer number (1738800).

Almost surely, 2^21172085 is an apocalyptic number.

It is an amenable number.

21172085 is a deficient number, since it is larger than the sum of its proper divisors (6648715).

21172085 is a wasteful number, since it uses less digits than its factorization.

21172085 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1468.

The product of its (nonzero) digits is 1120, while the sum is 26.

The square root of 21172085 is about 4601.3133994546. The cubic root of 21172085 is about 276.6439708161.

Adding to 21172085 its reverse (58027112), we get a palindrome (79199197).

The spelling of 21172085 in words is "twenty-one million, one hundred seventy-two thousand, eighty-five".