21687288 has 64 divisors (see below), whose sum is σ = 62415360. Its totient is φ = 6151296.

The previous prime is 21687287. The next prime is 21687301. The reversal of 21687288 is 88278612.

It is a Harshad number since it is a multiple of its sum of digits (42).

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 (21687287) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 27670 + ... + 28442.

It is an arithmetic number, because the mean of its divisors is an integer number (975240).

Almost surely, 2^21687288 is an apocalyptic number.

21687288 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21687288, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31207680).

21687288 is an abundant number, since it is smaller than the sum of its proper divisors (40728072).

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

21687288 is a wasteful number, since it uses less digits than its factorization.

21687288 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 956 (or 952 counting only the distinct ones).

The product of its digits is 86016, while the sum is 42.

The square root of 21687288 is about 4656.9612409811. The cubic root of 21687288 is about 278.8699693402.

The spelling of 21687288 in words is "twenty-one million, six hundred eighty-seven thousand, two hundred eighty-eight".