21271643 has 2 divisors, whose sum is σ = 21271644. Its totient is φ = 21271642.

The previous prime is 21271637. The next prime is 21271667. The reversal of 21271643 is 34617212.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21271643 is a prime.

It is a Sophie Germain prime.

It is not a weakly prime, because it can be changed into another prime (21271043) 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, 10635821 + 10635822.

It is an arithmetic number, because the mean of its divisors is an integer number (10635822).

Almost surely, 2^21271643 is an apocalyptic number.

21271643 is a deficient number, since it is larger than the sum of its proper divisors (1).

21271643 is an equidigital number, since it uses as much as digits as its factorization.

21271643 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2016, while the sum is 26.

The square root of 21271643 is about 4612.1191441679. The cubic root of 21271643 is about 277.0769160868.

Adding to 21271643 its reverse (34617212), we get a palindrome (55888855).

It can be divided in two parts, 212 and 71643, that multiplied together give a triangular number (15188316 = T₅₅₁₁).

The spelling of 21271643 in words is "twenty-one million, two hundred seventy-one thousand, six hundred forty-three".