21081569 has 2 divisors, whose sum is σ = 21081570. Its totient is φ = 21081568.

The previous prime is 21081559. The next prime is 21081589. The reversal of 21081569 is 96518012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13601344 + 7480225 = 3688^2 + 2735^2 .

It is a cyclic number.

It is not a de Polignac number, because 21081569 - 2²⁴ = 4304353 is a prime.

It is a super-2 number, since 2×21081569² = 888865103003522, which contains 22 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21081509) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10540784 + 10540785.

It is an arithmetic number, because the mean of its divisors is an integer number (10540785).

Almost surely, 2^21081569 is an apocalyptic number.

It is an amenable number.

21081569 is a deficient number, since it is larger than the sum of its proper divisors (1).

21081569 is an equidigital number, since it uses as much as digits as its factorization.

21081569 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 4320, while the sum is 32.

The square root of 21081569 is about 4591.4669769040. The cubic root of 21081569 is about 276.2491667495.

The spelling of 21081569 in words is "twenty-one million, eighty-one thousand, five hundred sixty-nine".