21643351 has 2 divisors, whose sum is σ = 21643352. Its totient is φ = 21643350.

The previous prime is 21643333. The next prime is 21643361. The reversal of 21643351 is 15334612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21643351 - 2¹¹ = 21641303 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21643331) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10821675 + 10821676.

It is an arithmetic number, because the mean of its divisors is an integer number (10821676).

Almost surely, 2^21643351 is an apocalyptic number.

21643351 is a deficient number, since it is larger than the sum of its proper divisors (1).

21643351 is an equidigital number, since it uses as much as digits as its factorization.

21643351 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2160, while the sum is 25.

The square root of 21643351 is about 4652.2415027597. The cubic root of 21643351 is about 278.6815180293.

Adding to 21643351 its reverse (15334612), we get a palindrome (36977963).

The spelling of 21643351 in words is "twenty-one million, six hundred forty-three thousand, three hundred fifty-one".