21217481 has 2 divisors, whose sum is σ = 21217482. Its totient is φ = 21217480.

The previous prime is 21217457. The next prime is 21217499. The reversal of 21217481 is 18471212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20976400 + 241081 = 4580^2 + 491^2 .

It is a cyclic number.

It is not a de Polignac number, because 21217481 - 2¹⁰ = 21216457 is a prime.

It is a super-2 number, since 2×21217481² = 900362999970722, which contains 22 as substring.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21217481.

It is not a weakly prime, because it can be changed into another prime (21217421) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10608740 + 10608741.

It is an arithmetic number, because the mean of its divisors is an integer number (10608741).

Almost surely, 2^21217481 is an apocalyptic number.

It is an amenable number.

21217481 is a deficient number, since it is larger than the sum of its proper divisors (1).

21217481 is an equidigital number, since it uses as much as digits as its factorization.

21217481 is an evil number, because the sum of its binary digits is even.

The product of its digits is 896, while the sum is 26.

The square root of 21217481 is about 4606.2436974177. The cubic root of 21217481 is about 276.8415511774.

Adding to 21217481 its reverse (18471212), we get a palindrome (39688693).

The spelling of 21217481 in words is "twenty-one million, two hundred seventeen thousand, four hundred eighty-one".