21423251 has 2 divisors, whose sum is σ = 21423252. Its totient is φ = 21423250.

The previous prime is 21423239. The next prime is 21423271. The reversal of 21423251 is 15232412.

It is an a-pointer prime, because the next prime (21423271) can be obtained adding 21423251 to its sum of digits (20).

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21423251 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21423221) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10711625 + 10711626.

It is an arithmetic number, because the mean of its divisors is an integer number (10711626).

Almost surely, 2^21423251 is an apocalyptic number.

21423251 is a deficient number, since it is larger than the sum of its proper divisors (1).

21423251 is an equidigital number, since it uses as much as digits as its factorization.

21423251 is an evil number, because the sum of its binary digits is even.

The product of its digits is 480, while the sum is 20.

The square root of 21423251 is about 4628.5257912212. The cubic root of 21423251 is about 277.7336224867.

Adding to 21423251 its reverse (15232412), we get a palindrome (36655663).

The spelling of 21423251 in words is "twenty-one million, four hundred twenty-three thousand, two hundred fifty-one".