21018869 has 2 divisors, whose sum is σ = 21018870. Its totient is φ = 21018868.

The previous prime is 21018859. The next prime is 21018929. The reversal of 21018869 is 96881012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20811844 + 207025 = 4562^2 + 455^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21018869 is a prime.

It is a super-2 number, since 2×21018869² = 883585708078322, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21018839) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10509434 + 10509435.

It is an arithmetic number, because the mean of its divisors is an integer number (10509435).

Almost surely, 2^21018869 is an apocalyptic number.

It is an amenable number.

21018869 is a deficient number, since it is larger than the sum of its proper divisors (1).

21018869 is an equidigital number, since it uses as much as digits as its factorization.

21018869 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 6912, while the sum is 35.

The square root of 21018869 is about 4584.6340093840. The cubic root of 21018869 is about 275.9750248702.

The spelling of 21018869 in words is "twenty-one million, eighteen thousand, eight hundred sixty-nine".