21695281 has 4 divisors (see below), whose sum is σ = 22971492. Its totient is φ = 20419072.

The previous prime is 21695269. The next prime is 21695291. The reversal of 21695281 is 18259612.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 12362256 + 9333025 = 3516^2 + 3055^2 .

It is a cyclic number.

It is not a de Polignac number, because 21695281 - 2¹³ = 21687089 is a prime.

It is a super-2 number, since 2×21695281² = 941370435337922, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21695221) 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 in 3 ways as a sum of consecutive naturals, for example, 638080 + ... + 638113.

It is an arithmetic number, because the mean of its divisors is an integer number (5742873).

Almost surely, 2^21695281 is an apocalyptic number.

It is an amenable number.

21695281 is a deficient number, since it is larger than the sum of its proper divisors (1276211).

21695281 is a wasteful number, since it uses less digits than its factorization.

21695281 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1276210.

The product of its digits is 8640, while the sum is 34.

The square root of 21695281 is about 4657.8193395622. The cubic root of 21695281 is about 278.9042249508.

The spelling of 21695281 in words is "twenty-one million, six hundred ninety-five thousand, two hundred eighty-one".