21809143 has 2 divisors, whose sum is σ = 21809144. Its totient is φ = 21809142.

The previous prime is 21809119. The next prime is 21809153. The reversal of 21809143 is 34190812.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21809143 - 2⁵ = 21809111 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21809153) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10904571 + 10904572.

It is an arithmetic number, because the mean of its divisors is an integer number (10904572).

Almost surely, 2^21809143 is an apocalyptic number.

21809143 is a deficient number, since it is larger than the sum of its proper divisors (1).

21809143 is an equidigital number, since it uses as much as digits as its factorization.

21809143 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1728, while the sum is 28.

The square root of 21809143 is about 4670.0260170581. The cubic root of 21809143 is about 279.3912924517.

Adding to 21809143 its reverse (34190812), we get a palindrome (55999955).

It can be divided in two parts, 21809 and 143, that added together give a cube (21952 = 28³).

The spelling of 21809143 in words is "twenty-one million, eight hundred nine thousand, one hundred forty-three".