21408943 has 2 divisors, whose sum is σ = 21408944. Its totient is φ = 21408942.

The previous prime is 21408913. The next prime is 21408949. The reversal of 21408943 is 34980412.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21408943 - 2¹³ = 21400751 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21408949) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10704471 + 10704472.

It is an arithmetic number, because the mean of its divisors is an integer number (10704472).

Almost surely, 2^21408943 is an apocalyptic number.

21408943 is a deficient number, since it is larger than the sum of its proper divisors (1).

21408943 is an equidigital number, since it uses as much as digits as its factorization.

21408943 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 6912, while the sum is 31.

The square root of 21408943 is about 4626.9799005399. The cubic root of 21408943 is about 277.6717785013.

The spelling of 21408943 in words is "twenty-one million, four hundred eight thousand, nine hundred forty-three".