21388769 has 2 divisors, whose sum is σ = 21388770. Its totient is φ = 21388768.

The previous prime is 21388751. The next prime is 21388777. The reversal of 21388769 is 96788312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20205025 + 1183744 = 4495^2 + 1088^2 .

It is a cyclic number.

It is not a de Polignac number, because 21388769 - 2¹² = 21384673 is a prime.

It is a super-2 number, since 2×21388769² = 914958878670722, which contains 22 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21388709) 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 as a sum of consecutive naturals, namely, 10694384 + 10694385.

It is an arithmetic number, because the mean of its divisors is an integer number (10694385).

Almost surely, 2^21388769 is an apocalyptic number.

It is an amenable number.

21388769 is a deficient number, since it is larger than the sum of its proper divisors (1).

21388769 is an equidigital number, since it uses as much as digits as its factorization.

21388769 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 145152, while the sum is 44.

The square root of 21388769 is about 4624.7993469987. The cubic root of 21388769 is about 277.5845328594.

The spelling of 21388769 in words is "twenty-one million, three hundred eighty-eight thousand, seven hundred sixty-nine".