18921807578061 has 6 divisors (see below), whose sum is σ = 27331499834990. Its totient is φ = 12614538385368.

The previous prime is 18921807578029. The next prime is 18921807578203. The reversal of 18921807578061 is 16087570812981.

It can be written as a sum of positive squares in only one way, i.e., 17804230884036 + 1117576694025 = 4219506^2 + 1057155^2 .

It is not a de Polignac number, because 18921807578061 - 2⁵ = 18921807578029 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 18921807578061.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18921807571061) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1051211532106 + ... + 1051211532123.

Almost surely, 2^{18921807578061} is an apocalyptic number.

It is an amenable number.

18921807578061 is a deficient number, since it is larger than the sum of its proper divisors (8409692256929).

18921807578061 is a wasteful number, since it uses less digits than its factorization.

18921807578061 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2102423064235 (or 2102423064232 counting only the distinct ones).

The product of its (nonzero) digits is 13547520, while the sum is 63.

The spelling of 18921807578061 in words is "eighteen trillion, nine hundred twenty-one billion, eight hundred seven million, five hundred seventy-eight thousand, sixty-one".