21981823 has 2 divisors, whose sum is σ = 21981824. Its totient is φ = 21981822.

The previous prime is 21981793. The next prime is 21981871. The reversal of 21981823 is 32818912.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21981823 - 2¹³ = 21973631 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21981893) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10990911 + 10990912.

It is an arithmetic number, because the mean of its divisors is an integer number (10990912).

Almost surely, 2^21981823 is an apocalyptic number.

21981823 is a deficient number, since it is larger than the sum of its proper divisors (1).

21981823 is an equidigital number, since it uses as much as digits as its factorization.

21981823 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 6912, while the sum is 34.

The square root of 21981823 is about 4688.4776847075. The cubic root of 21981823 is about 280.1267410918.

The spelling of 21981823 in words is "twenty-one million, nine hundred eighty-one thousand, eight hundred twenty-three".