21236251 has 2 divisors, whose sum is σ = 21236252. Its totient is φ = 21236250.

The previous prime is 21236249. The next prime is 21236263. The reversal of 21236251 is 15263212.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21236251 - 2¹ = 21236249 is a prime.

Together with 21236249, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21236651) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10618125 + 10618126.

It is an arithmetic number, because the mean of its divisors is an integer number (10618126).

Almost surely, 2^21236251 is an apocalyptic number.

21236251 is a deficient number, since it is larger than the sum of its proper divisors (1).

21236251 is an equidigital number, since it uses as much as digits as its factorization.

21236251 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 720, while the sum is 22.

The square root of 21236251 is about 4608.2806989158. The cubic root of 21236251 is about 276.9231628818.

Adding to 21236251 its reverse (15263212), we get a palindrome (36499463).

It can be divided in two parts, 212 and 36251, that added together give a palindrome (36463).

The spelling of 21236251 in words is "twenty-one million, two hundred thirty-six thousand, two hundred fifty-one".