18981661 has 2 divisors, whose sum is σ = 18981662. Its totient is φ = 18981660.

The previous prime is 18981649. The next prime is 18981667. The reversal of 18981661 is 16618981.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12320100 + 6661561 = 3510^2 + 2581^2 .

It is a cyclic number.

It is not a de Polignac number, because 18981661 - 2¹³ = 18973469 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18981667) by changing a digit.

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

It is a good prime.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9490830 + 9490831.

It is an arithmetic number, because the mean of its divisors is an integer number (9490831).

Almost surely, 2^18981661 is an apocalyptic number.

It is an amenable number.

18981661 is a deficient number, since it is larger than the sum of its proper divisors (1).

18981661 is an equidigital number, since it uses as much as digits as its factorization.

18981661 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 20736, while the sum is 40.

The square root of 18981661 is about 4356.7948081130. The cubic root of 18981661 is about 266.7542849235.

The spelling of 18981661 in words is "eighteen million, nine hundred eighty-one thousand, six hundred sixty-one".