21639388 has 6 divisors (see below), whose sum is σ = 37868936. Its totient is φ = 10819692.

The previous prime is 21639383. The next prime is 21639427. The reversal of 21639388 is 88393612.

It is a super-2 number, since 2×21639388² = 936526226029088, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21639388.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21639383) 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 as a sum of consecutive naturals, namely, 2704920 + ... + 2704927.

Almost surely, 2^21639388 is an apocalyptic number.

21639388 is the 2487-th centered heptagonal number.

It is an amenable number.

21639388 is a deficient number, since it is larger than the sum of its proper divisors (16229548).

21639388 is a wasteful number, since it uses less digits than its factorization.

21639388 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5409851 (or 5409849 counting only the distinct ones).

The product of its digits is 62208, while the sum is 40.

The square root of 21639388 is about 4651.8155595423. The cubic root of 21639388 is about 278.6645076894.

The spelling of 21639388 in words is "twenty-one million, six hundred thirty-nine thousand, three hundred eighty-eight".