21047281 has 2 divisors, whose sum is σ = 21047282. Its totient is φ = 21047280.

The previous prime is 21047237. The next prime is 21047303. The reversal of 21047281 is 18274012.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21013056 + 34225 = 4584^2 + 185^2 .

It is a cyclic number.

It is not a de Polignac number, because 21047281 - 2⁷ = 21047153 is a prime.

It is a super-2 number, since 2×21047281² = 885976074985922, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21047981) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10523640 + 10523641.

It is an arithmetic number, because the mean of its divisors is an integer number (10523641).

Almost surely, 2^21047281 is an apocalyptic number.

It is an amenable number.

21047281 is a deficient number, since it is larger than the sum of its proper divisors (1).

21047281 is an equidigital number, since it uses as much as digits as its factorization.

21047281 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 896, while the sum is 25.

The square root of 21047281 is about 4587.7315745366. The cubic root of 21047281 is about 276.0993175088.

The spelling of 21047281 in words is "twenty-one million, forty-seven thousand, two hundred eighty-one".