21981229 has 2 divisors, whose sum is σ = 21981230. Its totient is φ = 21981228.

The previous prime is 21981227. The next prime is 21981251. The reversal of 21981229 is 92218912.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15721225 + 6260004 = 3965^2 + 2502^2 .

It is a cyclic number.

It is not a de Polignac number, because 21981229 - 2¹ = 21981227 is a prime.

Together with 21981227, it forms a pair of twin primes.

It is a junction number, because it is equal to n+sod(n) for n = 21981194 and 21981203.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21981227) 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, 10990614 + 10990615.

It is an arithmetic number, because the mean of its divisors is an integer number (10990615).

Almost surely, 2^21981229 is an apocalyptic number.

It is an amenable number.

21981229 is a deficient number, since it is larger than the sum of its proper divisors (1).

21981229 is an equidigital number, since it uses as much as digits as its factorization.

21981229 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5184, while the sum is 34.

The square root of 21981229 is about 4688.4143374919. The cubic root of 21981229 is about 280.1242178436.

The spelling of 21981229 in words is "twenty-one million, nine hundred eighty-one thousand, two hundred twenty-nine".