21071251 has 2 divisors, whose sum is σ = 21071252. Its totient is φ = 21071250.

The previous prime is 21071249. The next prime is 21071257. The reversal of 21071251 is 15217012.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21071251 - 2¹ = 21071249 is a prime.

Together with 21071249, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21071257) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10535625 + 10535626.

It is an arithmetic number, because the mean of its divisors is an integer number (10535626).

Almost surely, 2^21071251 is an apocalyptic number.

21071251 is a deficient number, since it is larger than the sum of its proper divisors (1).

21071251 is an equidigital number, since it uses as much as digits as its factorization.

21071251 is an evil number, because the sum of its binary digits is even.

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

The square root of 21071251 is about 4590.3432333541. The cubic root of 21071251 is about 276.2040909766.

Adding to 21071251 its reverse (15217012), we get a palindrome (36288263).

The spelling of 21071251 in words is "twenty-one million, seventy-one thousand, two hundred fifty-one".