It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 12567777778 = 2 ⋅6283888889.
It is a 3-Lehmer number, since φ(87777776521) divides (87777776521-1)3.
It is a cyclic number.
It is a de Polignac number, because none of the positive numbers 2k-87777776521 is a prime.
It is a nialpdrome in base 10.
It is a Poulet number, since it divides 287777776520-1.
Almost surely, 287777776521 is an apocalyptic number.
87777776521 is the 139665-th centered nonagonal number.
It is an amenable number.
87777776521 is a wasteful number, since it uses less digits than its factorization.
87777776521 is an odious number, because the sum of its binary digits is odd.
The sum of its prime factors is 628490.
The spelling of 87777776521 in words is "eighty-seven billion, seven hundred seventy-seven million, seven hundred seventy-six thousand, five hundred twenty-one".