21706281 has 9 divisors (see below), whose sum is σ = 31373719. Its totient is φ = 14461536.

The previous prime is 21706259. The next prime is 21706313. The reversal of 21706281 is 18260712.

The square root of 21706281 is 4659.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 2205225 + 19501056 = 1485^2 + 4416^2 .

It is a tau number, because it is divible by the number of its divisors (9).

It is not a de Polignac number, because 21706281 - 2¹¹ = 21704233 is a prime.

It is a super-2 number, since 2×21706281² = 942325269701922, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21706211) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 13201 + ... + 14753.

Almost surely, 2^21706281 is an apocalyptic number.

21706281 is the 4659-th square number.

21706281 is the 2330-th centered octagonal number.

It is an amenable number.

21706281 is a deficient number, since it is larger than the sum of its proper divisors (9667438).

21706281 is an frugal number, since it uses more digits than its factorization.

21706281 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3112 (or 1556 counting only the distinct ones).

The product of its (nonzero) digits is 1344, while the sum is 27.

The cubic root of 21706281 is about 278.9513539112.

Adding to 21706281 its reverse (18260712), we get a palindrome (39966993).

The spelling of 21706281 in words is "twenty-one million, seven hundred six thousand, two hundred eighty-one".