21789281 has 2 divisors, whose sum is σ = 21789282. Its totient is φ = 21789280.

The previous prime is 21789241. The next prime is 21789289. The reversal of 21789281 is 18298712.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13808656 + 7980625 = 3716^2 + 2825^2 .

It is a cyclic number.

It is not a de Polignac number, because 21789281 - 2¹⁴ = 21772897 is a prime.

It is a super-2 number, since 2×21789281² = 949545532993922, which contains 22 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21789289) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10894640 + 10894641.

It is an arithmetic number, because the mean of its divisors is an integer number (10894641).

Almost surely, 2^21789281 is an apocalyptic number.

It is an amenable number.

21789281 is a deficient number, since it is larger than the sum of its proper divisors (1).

21789281 is an equidigital number, since it uses as much as digits as its factorization.

21789281 is an evil number, because the sum of its binary digits is even.

The product of its digits is 16128, while the sum is 38.

The square root of 21789281 is about 4667.8989920520. The cubic root of 21789281 is about 279.3064510420.

It can be divided in two parts, 217 and 89281, that added together give a palindrome (89498).

The spelling of 21789281 in words is "twenty-one million, seven hundred eighty-nine thousand, two hundred eighty-one".