21420643 has 2 divisors, whose sum is σ = 21420644. Its totient is φ = 21420642.

The previous prime is 21420587. The next prime is 21420649. The reversal of 21420643 is 34602412.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21420643 - 2⁹ = 21420131 is a prime.

It is not a weakly prime, because it can be changed into another prime (21420649) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10710321 + 10710322.

It is an arithmetic number, because the mean of its divisors is an integer number (10710322).

Almost surely, 2^21420643 is an apocalyptic number.

21420643 is a deficient number, since it is larger than the sum of its proper divisors (1).

21420643 is an equidigital number, since it uses as much as digits as its factorization.

21420643 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1152, while the sum is 22.

The square root of 21420643 is about 4628.2440514735. The cubic root of 21420643 is about 277.7223518866.

The spelling of 21420643 in words is "twenty-one million, four hundred twenty thousand, six hundred forty-three".