18861209 has 2 divisors, whose sum is σ = 18861210. Its totient is φ = 18861208.

The previous prime is 18861197. The next prime is 18861233. The reversal of 18861209 is 90216881.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15721225 + 3139984 = 3965^2 + 1772^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-18861209 is a prime.

It is a super-4 number, since 4×18861209⁴ (a number of 30 digits) contains 4444 as substring.

It is not a weakly prime, because it can be changed into another prime (18861709) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9430604 + 9430605.

It is an arithmetic number, because the mean of its divisors is an integer number (9430605).

Almost surely, 2^18861209 is an apocalyptic number.

It is an amenable number.

18861209 is a deficient number, since it is larger than the sum of its proper divisors (1).

18861209 is an equidigital number, since it uses as much as digits as its factorization.

18861209 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 18861209 is about 4342.9493434762. The cubic root of 18861209 is about 266.1888392804.

The spelling of 18861209 in words is "eighteen million, eight hundred sixty-one thousand, two hundred nine".