21129643 has 2 divisors, whose sum is σ = 21129644. Its totient is φ = 21129642.

The previous prime is 21129613. The next prime is 21129673. The reversal of 21129643 is 34692112.

It is a balanced prime because it is at equal distance from previous prime (21129613) and next prime (21129673).

It is a cyclic number.

It is not a de Polignac number, because 21129643 - 2⁹ = 21129131 is a prime.

It is not a weakly prime, because it can be changed into another prime (21129613) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10564821 + 10564822.

It is an arithmetic number, because the mean of its divisors is an integer number (10564822).

Almost surely, 2^21129643 is an apocalyptic number.

21129643 is a deficient number, since it is larger than the sum of its proper divisors (1).

21129643 is an equidigital number, since it uses as much as digits as its factorization.

21129643 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2592, while the sum is 28.

The square root of 21129643 is about 4596.6991417755. The cubic root of 21129643 is about 276.4589917459.

The spelling of 21129643 in words is "twenty-one million, one hundred twenty-nine thousand, six hundred forty-three".