21639172 has 6 divisors (see below), whose sum is σ = 37868558. Its totient is φ = 10819584.

The previous prime is 21639151. The next prime is 21639199. The reversal of 21639172 is 27193612.

It can be written as a sum of positive squares in only one way, i.e., 13205956 + 8433216 = 3634^2 + 2904^2 .

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2704893 + ... + 2704900.

Almost surely, 2^21639172 is an apocalyptic number.

It is an amenable number.

21639172 is a deficient number, since it is larger than the sum of its proper divisors (16229386).

21639172 is a wasteful number, since it uses less digits than its factorization.

21639172 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5409797 (or 5409795 counting only the distinct ones).

The product of its digits is 4536, while the sum is 31.

The square root of 21639172 is about 4651.7923427427. The cubic root of 21639172 is about 278.6635804954.

The spelling of 21639172 in words is "twenty-one million, six hundred thirty-nine thousand, one hundred seventy-two".