21501643 has 2 divisors, whose sum is σ = 21501644. Its totient is φ = 21501642.

The previous prime is 21501593. The next prime is 21501647. The reversal of 21501643 is 34610512.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21501643 - 2⁹ = 21501131 is a prime.

It is not a weakly prime, because it can be changed into another prime (21501647) 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, 10750821 + 10750822.

It is an arithmetic number, because the mean of its divisors is an integer number (10750822).

Almost surely, 2^21501643 is an apocalyptic number.

21501643 is a deficient number, since it is larger than the sum of its proper divisors (1).

21501643 is an equidigital number, since it uses as much as digits as its factorization.

21501643 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 720, while the sum is 22.

The square root of 21501643 is about 4636.9864136096. The cubic root of 21501643 is about 278.0719712559.

The spelling of 21501643 in words is "twenty-one million, five hundred one thousand, six hundred forty-three".