18807781 has 2 divisors, whose sum is σ = 18807782. Its totient is φ = 18807780.

The previous prime is 18807773. The next prime is 18807821. The reversal of 18807781 is 18770881.

It is an a-pointer prime, because the next prime (18807821) can be obtained adding 18807781 to its sum of digits (40).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17724100 + 1083681 = 4210^2 + 1041^2 .

It is an emirp because it is prime and its reverse (18770881) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 18807781 - 2³ = 18807773 is a prime.

It is a super-2 number, since 2×18807781² = 707465252287922, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18807181) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9403890 + 9403891.

It is an arithmetic number, because the mean of its divisors is an integer number (9403891).

Almost surely, 2^18807781 is an apocalyptic number.

It is an amenable number.

18807781 is a deficient number, since it is larger than the sum of its proper divisors (1).

18807781 is an equidigital number, since it uses as much as digits as its factorization.

18807781 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 25088, while the sum is 40.

The square root of 18807781 is about 4336.7938618293. The cubic root of 18807781 is about 265.9372578950.

The spelling of 18807781 in words is "eighteen million, eight hundred seven thousand, seven hundred eighty-one".