21781843 has 2 divisors, whose sum is σ = 21781844. Its totient is φ = 21781842.

The previous prime is 21781829. The next prime is 21781873. The reversal of 21781843 is 34818712.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21781843 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21781799 and 21781808.

It is not a weakly prime, because it can be changed into another prime (21781873) 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, 10890921 + 10890922.

It is an arithmetic number, because the mean of its divisors is an integer number (10890922).

Almost surely, 2^21781843 is an apocalyptic number.

21781843 is a deficient number, since it is larger than the sum of its proper divisors (1).

21781843 is an equidigital number, since it uses as much as digits as its factorization.

21781843 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 10752, while the sum is 34.

The square root of 21781843 is about 4667.1022058661. The cubic root of 21781843 is about 279.2746660278.

The spelling of 21781843 in words is "twenty-one million, seven hundred eighty-one thousand, eight hundred forty-three".