18778561 has 2 divisors, whose sum is σ = 18778562. Its totient is φ = 18778560.

The previous prime is 18778519. The next prime is 18778567. The reversal of 18778561 is 16587781.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14288400 + 4490161 = 3780^2 + 2119^2 .

It is a cyclic number.

It is not a de Polignac number, because 18778561 - 2⁷ = 18778433 is a prime.

It is not a weakly prime, because it can be changed into another prime (18778567) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9389280 + 9389281.

It is an arithmetic number, because the mean of its divisors is an integer number (9389281).

Almost surely, 2^18778561 is an apocalyptic number.

It is an amenable number.

18778561 is a deficient number, since it is larger than the sum of its proper divisors (1).

18778561 is an equidigital number, since it uses as much as digits as its factorization.

18778561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 94080, while the sum is 43.

The square root of 18778561 is about 4333.4237041859. The cubic root of 18778561 is about 265.7994653795.

The spelling of 18778561 in words is "eighteen million, seven hundred seventy-eight thousand, five hundred sixty-one".