21681228 has 12 divisors (see below), whose sum is σ = 50589560. Its totient is φ = 7227072.

The previous prime is 21681221. The next prime is 21681269. The reversal of 21681228 is 82218612.

It is a tau number, because it is divible by the number of its divisors (12).

It is a junction number, because it is equal to n+sod(n) for n = 21681195 and 21681204.

It is not an unprimeable number, because it can be changed into a prime (21681221) 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 3 ways as a sum of consecutive naturals, for example, 903373 + ... + 903396.

Almost surely, 2^21681228 is an apocalyptic number.

It is an amenable number.

21681228 is an abundant number, since it is smaller than the sum of its proper divisors (28908332).

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

21681228 is a wasteful number, since it uses less digits than its factorization.

21681228 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1806776 (or 1806774 counting only the distinct ones).

The product of its digits is 3072, while the sum is 30.

The square root of 21681228 is about 4656.3105566532. The cubic root of 21681228 is about 278.8439923801.

The spelling of 21681228 in words is "twenty-one million, six hundred eighty-one thousand, two hundred twenty-eight".