21729188 has 12 divisors (see below), whose sum is σ = 40951260. Its totient is φ = 10028832.

The previous prime is 21729161. The next prime is 21729199. The reversal of 21729188 is 88192712.

It can be written as a sum of positive squares in 2 ways, for example, as 11437924 + 10291264 = 3382^2 + 3208^2 .

It is a super-2 number, since 2×21729188² = 944315222278688, which contains 22 as substring.

It is an unprimeable number.

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 3 ways as a sum of consecutive naturals, for example, 208883 + ... + 208986.

It is an arithmetic number, because the mean of its divisors is an integer number (3412605).

Almost surely, 2^21729188 is an apocalyptic number.

It is an amenable number.

21729188 is a deficient number, since it is larger than the sum of its proper divisors (19222072).

21729188 is a wasteful number, since it uses less digits than its factorization.

21729188 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 417886 (or 417884 counting only the distinct ones).

The product of its digits is 16128, while the sum is 38.

The square root of 21729188 is about 4661.4577119180. The cubic root of 21729188 is about 279.0494467501.

The spelling of 21729188 in words is "twenty-one million, seven hundred twenty-nine thousand, one hundred eighty-eight".