18781661 has 2 divisors, whose sum is σ = 18781662. Its totient is φ = 18781660.

The previous prime is 18781643. The next prime is 18781667. The reversal of 18781661 is 16618781.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18748900 + 32761 = 4330^2 + 181^2 .

It is a cyclic number.

It is not a de Polignac number, because 18781661 - 2⁶ = 18781597 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18781667) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9390830 + 9390831.

It is an arithmetic number, because the mean of its divisors is an integer number (9390831).

Almost surely, 2^18781661 is an apocalyptic number.

It is an amenable number.

18781661 is a deficient number, since it is larger than the sum of its proper divisors (1).

18781661 is an equidigital number, since it uses as much as digits as its factorization.

18781661 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 16128, while the sum is 38.

The square root of 18781661 is about 4333.7813742735. The cubic root of 18781661 is about 265.8140907992.

The spelling of 18781661 in words is "eighteen million, seven hundred eighty-one thousand, six hundred sixty-one".