21172839 has 16 divisors (see below), whose sum is σ = 28926720. Its totient is φ = 13771520.

The previous prime is 21172829. The next prime is 21172849. The reversal of 21172839 is 93827112.

It is an interprime number because it is at equal distance from previous prime (21172829) and next prime (21172849).

It is a cyclic number.

It is not a de Polignac number, because 21172839 - 2⁵ = 21172807 is a prime.

It is a super-2 number, since 2×21172839² = 896578222639842, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21172819) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 22327 + ... + 23255.

It is an arithmetic number, because the mean of its divisors is an integer number (1807920).

Almost surely, 2^21172839 is an apocalyptic number.

21172839 is a deficient number, since it is larger than the sum of its proper divisors (7753881).

21172839 is a wasteful number, since it uses less digits than its factorization.

21172839 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1110.

The product of its digits is 6048, while the sum is 33.

The square root of 21172839 is about 4601.3953318532. The cubic root of 21172839 is about 276.6472548113.

The spelling of 21172839 in words is "twenty-one million, one hundred seventy-two thousand, eight hundred thirty-nine".