21131251 has 2 divisors, whose sum is σ = 21131252. Its totient is φ = 21131250.

The previous prime is 21131191. The next prime is 21131269. The reversal of 21131251 is 15213112.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21131251 is a prime.

It is not a weakly prime, because it can be changed into another prime (21131651) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10565625 + 10565626.

It is an arithmetic number, because the mean of its divisors is an integer number (10565626).

Almost surely, 2^21131251 is an apocalyptic number.

21131251 is a deficient number, since it is larger than the sum of its proper divisors (1).

21131251 is an equidigital number, since it uses as much as digits as its factorization.

21131251 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 60, while the sum is 16.

The square root of 21131251 is about 4596.8740465669. The cubic root of 21131251 is about 276.4660045601.

Adding to 21131251 its reverse (15213112), we get a palindrome (36344363).

It can be divided in two parts, 2113 and 1251, that added together give a square (3364 = 58²).

The spelling of 21131251 in words is "twenty-one million, one hundred thirty-one thousand, two hundred fifty-one".