251221 has 2 divisors, whose sum is σ = 251222. Its totient is φ = 251220.

The previous prime is 251219. The next prime is 251231. The reversal of 251221 is 122152.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 239121 + 12100 = 489^2 + 110^2 .

It is a cyclic number.

It is not a de Polignac number, because 251221 - 2¹ = 251219 is a prime.

It is a super-2 number, since 2×251221² = 126223981682, which contains 22 as substring.

Together with 251219, it forms a pair of twin primes.

It is a nialpdrome in base 4.

It is a zygodrome in base 4.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (251201) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 125610 + 125611.

It is an arithmetic number, because the mean of its divisors is an integer number (125611).

2²⁵¹²²¹ is an apocalyptic number.

It is an amenable number.

251221 is a deficient number, since it is larger than the sum of its proper divisors (1).

251221 is an equidigital number, since it uses as much as digits as its factorization.

251221 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 40, while the sum is 13.

The square root of 251221 is about 501.2195127886. The cubic root of 251221 is about 63.0984435560.

Adding to 251221 its reverse (122152), we get a palindrome (373373).

The spelling of 251221 in words is "two hundred fifty-one thousand, two hundred twenty-one".