21663828 has 24 divisors (see below), whose sum is σ = 56165760. Its totient is φ = 7221240.

The previous prime is 21663821. The next prime is 21663869. The reversal of 21663828 is 82836612.

21663828 is a `hidden beast` number, since 2 + 16 + 638 + 2 + 8 = 666.

It is a super-2 number, since 2×21663828² = 938642887227168, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a junction number, because it is equal to n+sod(n) for n = 21663792 and 21663801.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21663821) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 100188 + ... + 100403.

It is an arithmetic number, because the mean of its divisors is an integer number (2340240).

Almost surely, 2^21663828 is an apocalyptic number.

It is an amenable number.

21663828 is an abundant number, since it is smaller than the sum of its proper divisors (34501932).

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

21663828 is a wasteful number, since it uses less digits than its factorization.

21663828 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 200604 (or 200596 counting only the distinct ones).

The product of its digits is 27648, while the sum is 36.

The square root of 21663828 is about 4654.4417495549. The cubic root of 21663828 is about 278.7693781564.

The spelling of 21663828 in words is "twenty-one million, six hundred sixty-three thousand, eight hundred twenty-eight".