18681515977661 has 2 divisors, whose sum is σ = 18681515977662. Its totient is φ = 18681515977660.

The previous prime is 18681515977633. The next prime is 18681515977681. The reversal of 18681515977661 is 16677951518681.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15310050793636 + 3371465184025 = 3912806^2 + 1836155^2 .

It is a cyclic number.

It is not a de Polignac number, because 18681515977661 - 2¹⁰ = 18681515976637 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18681515977681) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9340757988830 + 9340757988831.

It is an arithmetic number, because the mean of its divisors is an integer number (9340757988831).

Almost surely, 2^{18681515977661} is an apocalyptic number.

It is an amenable number.

18681515977661 is a deficient number, since it is larger than the sum of its proper divisors (1).

18681515977661 is an equidigital number, since it uses as much as digits as its factorization.

18681515977661 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 152409600, while the sum is 71.

The spelling of 18681515977661 in words is "eighteen trillion, six hundred eighty-one billion, five hundred fifteen million, nine hundred seventy-seven thousand, six hundred sixty-one".