20688281 has 4 divisors (see below), whose sum is σ = 21401700. Its totient is φ = 19974864.

The previous prime is 20688277. The next prime is 20688287. The reversal of 20688281 is 18288602.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 9665881 + 11022400 = 3109^2 + 3320^2 .

It is a cyclic number.

It is not a de Polignac number, because 20688281 - 2² = 20688277 is a prime.

It is a super-2 number, since 2×20688281² = 856009941469922, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20688287) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 356666 + ... + 356723.

It is an arithmetic number, because the mean of its divisors is an integer number (5350425).

Almost surely, 2^20688281 is an apocalyptic number.

It is an amenable number.

20688281 is a deficient number, since it is larger than the sum of its proper divisors (713419).

20688281 is an equidigital number, since it uses as much as digits as its factorization.

20688281 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 713418.

The product of its (nonzero) digits is 12288, while the sum is 35.

The square root of 20688281 is about 4548.4372041395. The cubic root of 20688281 is about 274.5205132187.

The spelling of 20688281 in words is "twenty million, six hundred eighty-eight thousand, two hundred eighty-one".