1989

This number is a composite.

In the year 1989, the largest known prime was the 65087-digit prime 391581 * (2^216193 - 1), as established by John Brown, Landon Curt Noll, Bodo Parady, Gene Smith, Joel Smith, and Sergio Zarantonello: "The Amdahl Six." Note that 391581's reversal is a cube: 185193 = 57^3 = 3^3 * 19^3, that 216193 = 41 * 5273 is semiprime, and that the digit-length is a 3-brilliant number: 65087 = 11 * 61 * 97. [Andrew]