21688237 has 2 divisors, whose sum is σ = 21688238. Its totient is φ = 21688236.

The previous prime is 21688217. The next prime is 21688279. The reversal of 21688237 is 73288612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20666116 + 1022121 = 4546^2 + 1011^2 .

It is a cyclic number.

It is not a de Polignac number, because 21688237 - 2⁷ = 21688109 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21688196 and 21688205.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21688217) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10844118 + 10844119.

It is an arithmetic number, because the mean of its divisors is an integer number (10844119).

Almost surely, 2^21688237 is an apocalyptic number.

It is an amenable number.

21688237 is a deficient number, since it is larger than the sum of its proper divisors (1).

21688237 is an equidigital number, since it uses as much as digits as its factorization.

21688237 is an evil number, because the sum of its binary digits is even.

The product of its digits is 32256, while the sum is 37.

The square root of 21688237 is about 4657.0631303430. The cubic root of 21688237 is about 278.8740369110.

The spelling of 21688237 in words is "twenty-one million, six hundred eighty-eight thousand, two hundred thirty-seven".