21391543 has 2 divisors, whose sum is σ = 21391544. Its totient is φ = 21391542.

The previous prime is 21391523. The next prime is 21391567. The reversal of 21391543 is 34519312.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21391543 is a prime.

It is a super-2 number, since 2×21391543² = 915196223841698, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21391523) 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, 10695771 + 10695772.

It is an arithmetic number, because the mean of its divisors is an integer number (10695772).

Almost surely, 2^21391543 is an apocalyptic number.

21391543 is a deficient number, since it is larger than the sum of its proper divisors (1).

21391543 is an equidigital number, since it uses as much as digits as its factorization.

21391543 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3240, while the sum is 28.

The square root of 21391543 is about 4625.0992421785. The cubic root of 21391543 is about 277.5965327117.

The spelling of 21391543 in words is "twenty-one million, three hundred ninety-one thousand, five hundred forty-three".