21669281 has 2 divisors, whose sum is σ = 21669282. Its totient is φ = 21669280.

The previous prime is 21669269. The next prime is 21669299. The reversal of 21669281 is 18296612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21669025 + 256 = 4655^2 + 16^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21669281 is a prime.

It is a super-2 number, since 2×21669281² = 939115478113922, which contains 22 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21669211) 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 as a sum of consecutive naturals, namely, 10834640 + 10834641.

It is an arithmetic number, because the mean of its divisors is an integer number (10834641).

Almost surely, 2^21669281 is an apocalyptic number.

It is an amenable number.

21669281 is a deficient number, since it is larger than the sum of its proper divisors (1).

21669281 is an equidigital number, since it uses as much as digits as its factorization.

21669281 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 10368, while the sum is 35.

The square root of 21669281 is about 4655.0274972335. The cubic root of 21669281 is about 278.7927658651.

The spelling of 21669281 in words is "twenty-one million, six hundred sixty-nine thousand, two hundred eighty-one".