21281716 has 12 divisors (see below), whose sum is σ = 38862432. Its totient is φ = 10178168.

The previous prime is 21281707. The next prime is 21281719. The reversal of 21281716 is 61718212.

It is a super-2 number, since 2×21281716² = 905822871809312, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21281719) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 115570 + ... + 115753.

It is an arithmetic number, because the mean of its divisors is an integer number (3238536).

Almost surely, 2^21281716 is an apocalyptic number.

It is an amenable number.

21281716 is a deficient number, since it is larger than the sum of its proper divisors (17580716).

21281716 is a wasteful number, since it uses less digits than its factorization.

21281716 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 231350 (or 231348 counting only the distinct ones).

The product of its digits is 1344, while the sum is 28.

The square root of 21281716 is about 4613.2110292073. The cubic root of 21281716 is about 277.1206449663.

Adding to 21281716 its reverse (61718212), we get a palindrome (82999928).

It can be divided in two parts, 2128 and 1716, that added together give a square (3844 = 62²).

The spelling of 21281716 in words is "twenty-one million, two hundred eighty-one thousand, seven hundred sixteen".