21181872 has 40 divisors (see below), whose sum is σ = 54885376. Its totient is φ = 7039296.

The previous prime is 21181837. The next prime is 21181877. The reversal of 21181872 is 27818112.

It is a happy number.

It is not an unprimeable number, because it can be changed into a prime (21181877) 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 7 ways as a sum of consecutive naturals, for example, 28773 + ... + 29499.

Almost surely, 2^21181872 is an apocalyptic number.

It is an amenable number.

21181872 is an abundant number, since it is smaller than the sum of its proper divisors (33703504).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21181872 is a wasteful number, since it uses less digits than its factorization.

21181872 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1345 (or 1339 counting only the distinct ones).

The product of its digits is 1792, while the sum is 30.

The square root of 21181872 is about 4602.3767772750. The cubic root of 21181872 is about 276.6865913619.

Adding to 21181872 its reverse (27818112), we get a palindrome (48999984).

The spelling of 21181872 in words is "twenty-one million, one hundred eighty-one thousand, eight hundred seventy-two".