21284381 has 2 divisors, whose sum is σ = 21284382. Its totient is φ = 21284380.

The previous prime is 21284369. The next prime is 21284387. The reversal of 21284381 is 18348212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13388281 + 7896100 = 3659^2 + 2810^2 .

It is a cyclic number.

It is not a de Polignac number, because 21284381 - 2¹⁴ = 21267997 is a prime.

It is a super-2 number, since 2×21284381² = 906049749106322, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is equal to p_1346807 and since 21284381 and 1346807 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21284387) 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, 10642190 + 10642191.

It is an arithmetic number, because the mean of its divisors is an integer number (10642191).

Almost surely, 2^21284381 is an apocalyptic number.

It is an amenable number.

21284381 is a deficient number, since it is larger than the sum of its proper divisors (1).

21284381 is an equidigital number, since it uses as much as digits as its factorization.

21284381 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3072, while the sum is 29.

The square root of 21284381 is about 4613.4998645280. The cubic root of 21284381 is about 277.1322119486.

The spelling of 21284381 in words is "twenty-one million, two hundred eighty-four thousand, three hundred eighty-one".