18777961721561 has 16 divisors (see below), whose sum is σ = 22590175964160. Its totient is φ = 15248170561680.

The previous prime is 18777961721543. The next prime is 18777961721587. The reversal of 18777961721561 is 16512716977781.

It is a happy number.

It is a de Polignac number, because none of the positive numbers 2^k-18777961721561 is a prime.

It is a super-2 number, since 2×18777961721561² (a number of 27 digits) contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 18777961721491 and 18777961721500.

It is not an unprimeable number, because it can be changed into a prime (18777961721501) 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 15 ways as a sum of consecutive naturals, for example, 25641890 + ... + 26364036.

It is an arithmetic number, because the mean of its divisors is an integer number (1411885997760).

Almost surely, 2^{18777961721561} is an apocalyptic number.

It is an amenable number.

18777961721561 is a deficient number, since it is larger than the sum of its proper divisors (3812214242599).

18777961721561 is a wasteful number, since it uses less digits than its factorization.

18777961721561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 917684.

The product of its digits is 62233920, while the sum is 68.

The spelling of 18777961721561 in words is "eighteen trillion, seven hundred seventy-seven billion, nine hundred sixty-one million, seven hundred twenty-one thousand, five hundred sixty-one".