21281688 has 48 divisors (see below), whose sum is σ = 61031880. Its totient is φ = 6676224.

The previous prime is 21281683. The next prime is 21281707. The reversal of 21281688 is 88618212.

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

It is a nude number because it is divisible by every one of its digits.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21281683) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 7470 + ... + 9917.

Almost surely, 2^21281688 is an apocalyptic number.

It is an amenable number.

21281688 is an abundant number, since it is smaller than the sum of its proper divisors (39750192).

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

21281688 is a wasteful number, since it uses less digits than its factorization.

21281688 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17416 (or 17409 counting only the distinct ones).

The product of its digits is 12288, while the sum is 36.

The square root of 21281688 is about 4613.2079944438. The cubic root of 21281688 is about 277.1205234319.

The spelling of 21281688 in words is "twenty-one million, two hundred eighty-one thousand, six hundred eighty-eight".