21611251 has 2 divisors, whose sum is σ = 21611252. Its totient is φ = 21611250.

The previous prime is 21611243. The next prime is 21611257. The reversal of 21611251 is 15211612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21611251 - 2³ = 21611243 is a prime.

It is not a weakly prime, because it can be changed into another prime (21611257) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10805625 + 10805626.

It is an arithmetic number, because the mean of its divisors is an integer number (10805626).

Almost surely, 2^21611251 is an apocalyptic number.

21611251 is a deficient number, since it is larger than the sum of its proper divisors (1).

21611251 is an equidigital number, since it uses as much as digits as its factorization.

21611251 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 120, while the sum is 19.

The square root of 21611251 is about 4648.7902727484. The cubic root of 21611251 is about 278.5436758051.

Adding to 21611251 its reverse (15211612), we get a palindrome (36822863).

The spelling of 21611251 in words is "twenty-one million, six hundred eleven thousand, two hundred fifty-one".