21395251 has 2 divisors, whose sum is σ = 21395252. Its totient is φ = 21395250.

The previous prime is 21395249. The next prime is 21395261. The reversal of 21395251 is 15259312.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21395251 - 2¹ = 21395249 is a prime.

Together with 21395249, it forms a pair of twin primes.

It is the 4626-th Hogben number.

It is not a weakly prime, because it can be changed into another prime (21395261) by changing a digit.

It is a nontrivial repunit in base 4625.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10697625 + 10697626.

It is an arithmetic number, because the mean of its divisors is an integer number (10697626).

Almost surely, 2^21395251 is an apocalyptic number.

21395251 is a deficient number, since it is larger than the sum of its proper divisors (1).

21395251 is an equidigital number, since it uses as much as digits as its factorization.

21395251 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2700, while the sum is 28.

The square root of 21395251 is about 4625.5000810723. The cubic root of 21395251 is about 277.6125712692.

The spelling of 21395251 in words is "twenty-one million, three hundred ninety-five thousand, two hundred fifty-one".