18781921 has 2 divisors, whose sum is σ = 18781922. Its totient is φ = 18781920.

The previous prime is 18781913. The next prime is 18781967. The reversal of 18781921 is 12918781.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13542400 + 5239521 = 3680^2 + 2289^2 .

It is a cyclic number.

It is not a de Polignac number, because 18781921 - 2³ = 18781913 is a prime.

It is not a weakly prime, because it can be changed into another prime (18781121) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9390960 + 9390961.

It is an arithmetic number, because the mean of its divisors is an integer number (9390961).

Almost surely, 2^18781921 is an apocalyptic number.

It is an amenable number.

18781921 is a deficient number, since it is larger than the sum of its proper divisors (1).

18781921 is an equidigital number, since it uses as much as digits as its factorization.

18781921 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 8064, while the sum is 37.

The square root of 18781921 is about 4333.8113710682. The cubic root of 18781921 is about 265.8153173742.

The spelling of 18781921 in words is "eighteen million, seven hundred eighty-one thousand, nine hundred twenty-one".