21717481 has 4 divisors (see below), whose sum is σ = 21773700. Its totient is φ = 21661264.

The previous prime is 21717473. The next prime is 21717523. The reversal of 21717481 is 18471712.

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 7155625 + 14561856 = 2675^2 + 3816^2 .

It is a cyclic number.

It is not a de Polignac number, because 21717481 - 2³ = 21717473 is a prime.

It is a super-2 number, since 2×21717481² = 943297961970722, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21717461) 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, 27526 + ... + 28303.

It is an arithmetic number, because the mean of its divisors is an integer number (5443425).

Almost surely, 2^21717481 is an apocalyptic number.

It is an amenable number.

21717481 is a deficient number, since it is larger than the sum of its proper divisors (56219).

21717481 is an equidigital number, since it uses as much as digits as its factorization.

21717481 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 56218.

The product of its digits is 3136, while the sum is 31.

The square root of 21717481 is about 4660.2018196640. The cubic root of 21717481 is about 278.9993234055. Note that the first 3 decimals are identical.

The spelling of 21717481 in words is "twenty-one million, seven hundred seventeen thousand, four hundred eighty-one".