21707281 has 2 divisors, whose sum is σ = 21707282. Its totient is φ = 21707280.

The previous prime is 21707267. The next prime is 21707293. The reversal of 21707281 is 18270712.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17297281 + 4410000 = 4159^2 + 2100^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21707281 is a prime.

It is a super-2 number, since 2×21707281² = 942412096825922, which contains 22 as substring.

It is equal to p_1371871 and since 21707281 and 1371871 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (21707201) 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, 10853640 + 10853641.

It is an arithmetic number, because the mean of its divisors is an integer number (10853641).

Almost surely, 2^21707281 is an apocalyptic number.

It is an amenable number.

21707281 is a deficient number, since it is larger than the sum of its proper divisors (1).

21707281 is an equidigital number, since it uses as much as digits as its factorization.

21707281 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1568, while the sum is 28.

The square root of 21707281 is about 4659.1073179312. The cubic root of 21707281 is about 278.9556375725.

Adding to 21707281 its reverse (18270712), we get a palindrome (39977993).

The spelling of 21707281 in words is "twenty-one million, seven hundred seven thousand, two hundred eighty-one".