21688145 has 8 divisors (see below), whose sum is σ = 26177256. Its totient is φ = 17249536.

The previous prime is 21688111. The next prime is 21688159. The reversal of 21688145 is 54188612.

It can be written as a sum of positive squares in 4 ways, for example, as 5180176 + 16507969 = 2276^2 + 4063^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21688145 - 2²⁰ = 20639569 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 11672 + ... + 13401.

It is an arithmetic number, because the mean of its divisors is an integer number (3272157).

Almost surely, 2^21688145 is an apocalyptic number.

It is an amenable number.

21688145 is a deficient number, since it is larger than the sum of its proper divisors (4489111).

21688145 is a wasteful number, since it uses less digits than its factorization.

21688145 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 25251.

The product of its digits is 15360, while the sum is 35.

The square root of 21688145 is about 4657.0532528628. The cubic root of 21688145 is about 278.8736425890.

The spelling of 21688145 in words is "twenty-one million, six hundred eighty-eight thousand, one hundred forty-five".