21406237 has 2 divisors, whose sum is σ = 21406238. Its totient is φ = 21406236.

The previous prime is 21406207. The next prime is 21406241. The reversal of 21406237 is 73260412.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21104836 + 301401 = 4594^2 + 549^2 .

It is a cyclic number.

It is not a de Polignac number, because 21406237 - 2⁷ = 21406109 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21406207) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10703118 + 10703119.

It is an arithmetic number, because the mean of its divisors is an integer number (10703119).

Almost surely, 2^21406237 is an apocalyptic number.

It is an amenable number.

21406237 is a deficient number, since it is larger than the sum of its proper divisors (1).

21406237 is an equidigital number, since it uses as much as digits as its factorization.

21406237 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2016, while the sum is 25.

The square root of 21406237 is about 4626.6874759378. The cubic root of 21406237 is about 277.6600791616.

Adding to 21406237 its reverse (73260412), we get a palindrome (94666649).

The spelling of 21406237 in words is "twenty-one million, four hundred six thousand, two hundred thirty-seven".