21390043 has 2 divisors, whose sum is σ = 21390044. Its totient is φ = 21390042.

The previous prime is 21390041. The next prime is 21390071. The reversal of 21390043 is 34009312.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21390043 - 2¹ = 21390041 is a prime.

Together with 21390041, it forms a pair of twin primes.

It is a junction number, because it is equal to n+sod(n) for n = 21389996 and 21390023.

It is not a weakly prime, because it can be changed into another prime (21390041) 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, 10695021 + 10695022.

It is an arithmetic number, because the mean of its divisors is an integer number (10695022).

Almost surely, 2^21390043 is an apocalyptic number.

21390043 is a deficient number, since it is larger than the sum of its proper divisors (1).

21390043 is an equidigital number, since it uses as much as digits as its factorization.

21390043 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 648, while the sum is 22.

The square root of 21390043 is about 4624.9370806531. The cubic root of 21390043 is about 277.5900440956.

Adding to 21390043 its reverse (34009312), we get a palindrome (55399355).

The spelling of 21390043 in words is "twenty-one million, three hundred ninety thousand, forty-three".