21120251 has 2 divisors, whose sum is σ = 21120252. Its totient is φ = 21120250.

The previous prime is 21120223. The next prime is 21120257. The reversal of 21120251 is 15202112.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21120251 - 2¹⁸ = 20858107 is a prime.

It is a Sophie Germain prime.

It is not a weakly prime, because it can be changed into another prime (21120257) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10560125 + 10560126.

It is an arithmetic number, because the mean of its divisors is an integer number (10560126).

Almost surely, 2^21120251 is an apocalyptic number.

21120251 is a deficient number, since it is larger than the sum of its proper divisors (1).

21120251 is an equidigital number, since it uses as much as digits as its factorization.

21120251 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 40, while the sum is 14.

The square root of 21120251 is about 4595.6774255816. The cubic root of 21120251 is about 276.4180242190.

Adding to 21120251 its reverse (15202112), we get a palindrome (36322363).

The spelling of 21120251 in words is "twenty-one million, one hundred twenty thousand, two hundred fifty-one".