21710251 has 2 divisors, whose sum is σ = 21710252. Its totient is φ = 21710250.

The previous prime is 21710239. The next prime is 21710267. The reversal of 21710251 is 15201712.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21710251 - 2⁷ = 21710123 is a prime.

It is not a weakly prime, because it can be changed into another prime (21710201) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10855125 + 10855126.

It is an arithmetic number, because the mean of its divisors is an integer number (10855126).

Almost surely, 2^21710251 is an apocalyptic number.

21710251 is a deficient number, since it is larger than the sum of its proper divisors (1).

21710251 is an equidigital number, since it uses as much as digits as its factorization.

21710251 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 140, while the sum is 19.

The square root of 21710251 is about 4659.4260376145. The cubic root of 21710251 is about 278.9683592712.

Adding to 21710251 its reverse (15201712), we get a palindrome (36911963).

The spelling of 21710251 in words is "twenty-one million, seven hundred ten thousand, two hundred fifty-one".