251521421 has 2 divisors, whose sum is σ = 251521422. Its totient is φ = 251521420.

The previous prime is 251521363. The next prime is 251521423. The reversal of 251521421 is 124125152.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 160528900 + 90992521 = 12670^2 + 9539^2 .

It is a cyclic number.

It is not a de Polignac number, because 251521421 - 2¹⁰ = 251520397 is a prime.

Together with 251521423, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (251521423) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 125760710 + 125760711.

It is an arithmetic number, because the mean of its divisors is an integer number (125760711).

Almost surely, 2^251521421 is an apocalyptic number.

It is an amenable number.

251521421 is a deficient number, since it is larger than the sum of its proper divisors (1).

251521421 is an equidigital number, since it uses as much as digits as its factorization.

251521421 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 800, while the sum is 23.

The square root of 251521421 is about 15859.4268811959. The cubic root of 251521421 is about 631.2358549129.

Adding to 251521421 its reverse (124125152), we get a palindrome (375646573).

The spelling of 251521421 in words is "two hundred fifty-one million, five hundred twenty-one thousand, four hundred twenty-one".