21380981 has 2 divisors, whose sum is σ = 21380982. Its totient is φ = 21380980.

The previous prime is 21380977. The next prime is 21381037. The reversal of 21380981 is 18908312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21252100 + 128881 = 4610^2 + 359^2 .

It is a cyclic number.

It is not a de Polignac number, because 21380981 - 2² = 21380977 is a prime.

It is a super-2 number, since 2×21380981² = 914292697044722, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21380921) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10690490 + 10690491.

It is an arithmetic number, because the mean of its divisors is an integer number (10690491).

Almost surely, 2^21380981 is an apocalyptic number.

It is an amenable number.

21380981 is a deficient number, since it is larger than the sum of its proper divisors (1).

21380981 is an equidigital number, since it uses as much as digits as its factorization.

21380981 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 3456, while the sum is 32.

The square root of 21380981 is about 4623.9572878650. The cubic root of 21380981 is about 277.5508377493.

The spelling of 21380981 in words is "twenty-one million, three hundred eighty thousand, nine hundred eighty-one".