21143981 has 2 divisors, whose sum is σ = 21143982. Its totient is φ = 21143980.

The previous prime is 21143977. The next prime is 21143999. The reversal of 21143981 is 18934112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20884900 + 259081 = 4570^2 + 509^2 .

It is a cyclic number.

It is not a de Polignac number, because 21143981 - 2² = 21143977 is a prime.

It is a super-2 number, since 2×21143981² = 894135865056722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21143911) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10571990 + 10571991.

It is an arithmetic number, because the mean of its divisors is an integer number (10571991).

Almost surely, 2^21143981 is an apocalyptic number.

It is an amenable number.

21143981 is a deficient number, since it is larger than the sum of its proper divisors (1).

21143981 is an equidigital number, since it uses as much as digits as its factorization.

21143981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1728, while the sum is 29.

The square root of 21143981 is about 4598.2584746836. The cubic root of 21143981 is about 276.5215101199.

The spelling of 21143981 in words is "twenty-one million, one hundred forty-three thousand, nine hundred eighty-one".