21551251 has 2 divisors, whose sum is σ = 21551252. Its totient is φ = 21551250.

The previous prime is 21551221. The next prime is 21551267. The reversal of 21551251 is 15215512.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21551251 is a prime.

It is not a weakly prime, because it can be changed into another prime (21551221) 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, 10775625 + 10775626.

It is an arithmetic number, because the mean of its divisors is an integer number (10775626).

Almost surely, 2^21551251 is an apocalyptic number.

21551251 is a deficient number, since it is larger than the sum of its proper divisors (1).

21551251 is an equidigital number, since it uses as much as digits as its factorization.

21551251 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 500, while the sum is 22.

The square root of 21551251 is about 4642.3324956319. The cubic root of 21551251 is about 278.2856603383.

Adding to 21551251 its reverse (15215512), we get a palindrome (36766763).

The spelling of 21551251 in words is "twenty-one million, five hundred fifty-one thousand, two hundred fifty-one".