21251643 has 12 divisors (see below), whose sum is σ = 32961960. Its totient is φ = 12143712.

The previous prime is 21251617. The next prime is 21251669. The reversal of 21251643 is 34615212.

It is an interprime number because it is at equal distance from previous prime (21251617) and next prime (21251669).

It is not a de Polignac number, because 21251643 - 2⁵ = 21251611 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21251543) 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 in 11 ways as a sum of consecutive naturals, for example, 72138 + ... + 72431.

It is an arithmetic number, because the mean of its divisors is an integer number (2746830).

Almost surely, 2^21251643 is an apocalyptic number.

21251643 is a deficient number, since it is larger than the sum of its proper divisors (11710317).

21251643 is a wasteful number, since it uses less digits than its factorization.

21251643 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 144586 (or 144579 counting only the distinct ones).

The product of its digits is 1440, while the sum is 24.

The square root of 21251643 is about 4609.9504335730. The cubic root of 21251643 is about 276.9900512095.

Adding to 21251643 its reverse (34615212), we get a palindrome (55866855).

The spelling of 21251643 in words is "twenty-one million, two hundred fifty-one thousand, six hundred forty-three".