21688291 has 16 divisors (see below), whose sum is σ = 23616000. Its totient is φ = 19852128.

The previous prime is 21688283. The next prime is 21688301. The reversal of 21688291 is 19288612.

21688291 = 63³ + 64³ + ... + 100³.

It is a cyclic number.

It is not a de Polignac number, because 21688291 - 2³ = 21688283 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21688291.

It is not an unprimeable number, because it can be changed into a prime (21688391) 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, 132976 + ... + 133138.

It is an arithmetic number, because the mean of its divisors is an integer number (1476000).

Almost surely, 2^21688291 is an apocalyptic number.

21688291 is a deficient number, since it is larger than the sum of its proper divisors (1927709).

21688291 is a wasteful number, since it uses less digits than its factorization.

21688291 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 378.

The product of its digits is 13824, while the sum is 37.

The square root of 21688291 is about 4657.0689279846. The cubic root of 21688291 is about 278.8742683604.

The spelling of 21688291 in words is "twenty-one million, six hundred eighty-eight thousand, two hundred ninety-one".