21171251 has 2 divisors, whose sum is σ = 21171252. Its totient is φ = 21171250.

The previous prime is 21171217. The next prime is 21171253. The reversal of 21171251 is 15217112.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21171251 - 2¹⁴ = 21154867 is a prime.

Together with 21171253, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21171253) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10585625 + 10585626.

It is an arithmetic number, because the mean of its divisors is an integer number (10585626).

Almost surely, 2^21171251 is an apocalyptic number.

21171251 is a deficient number, since it is larger than the sum of its proper divisors (1).

21171251 is an equidigital number, since it uses as much as digits as its factorization.

21171251 is an evil number, because the sum of its binary digits is even.

The product of its digits is 140, while the sum is 20.

The square root of 21171251 is about 4601.2227722639. Note that the first 3 decimals coincide. The cubic root of 21171251 is about 276.6403382956.

Adding to 21171251 its reverse (15217112), we get a palindrome (36388363).

The spelling of 21171251 in words is "twenty-one million, one hundred seventy-one thousand, two hundred fifty-one".