21768569 has 2 divisors, whose sum is σ = 21768570. Its totient is φ = 21768568.

The previous prime is 21768563. The next prime is 21768583. The reversal of 21768569 is 96586712.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16104169 + 5664400 = 4013^2 + 2380^2 .

It is a cyclic number.

It is not a de Polignac number, because 21768569 - 2⁴ = 21768553 is a prime.

It is a super-2 number, since 2×21768569² = 947741192615522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21768563) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10884284 + 10884285.

It is an arithmetic number, because the mean of its divisors is an integer number (10884285).

Almost surely, 2^21768569 is an apocalyptic number.

It is an amenable number.

21768569 is a deficient number, since it is larger than the sum of its proper divisors (1).

21768569 is an equidigital number, since it uses as much as digits as its factorization.

21768569 is an evil number, because the sum of its binary digits is even.

The product of its digits is 181440, while the sum is 44.

The square root of 21768569 is about 4665.6799075805. The cubic root of 21768569 is about 279.2179238869.

It can be divided in two parts, 217 and 68569, that added together give a palindrome (68786).

The spelling of 21768569 in words is "twenty-one million, seven hundred sixty-eight thousand, five hundred sixty-nine".