Graham's number is a tremendously large finite number that is a proven upper bound to the solution of a certain problem in Ramsey theory. It is named after mathematician Ronald Graham who used the number as a simplified explanation of the upper bounds of the problem he was working on in conversations with popular science writer Martin Gardner. The number was published in the 1980 Guinness Book of World Records, which added to the popular interest in the number. Graham's number is much larger than any other number you can imagine. It is so large that the observable universe is far too small to contain an ordinary digital representation of Graham's number, assuming that each digit occupies one Planck volume which equals to about 4.2217 × 10 − 105 m 3 4.2217×10 −105 m 3 . Even power towers of the form a b c ⋅ ⋅ ⋅ a b c ⋅ ⋅ ⋅ are insufficient for this purpose, although it can be described by recursive formulas using Knuth's up-arrow notation. Though too large to be computed in full, many of the last digits of Graham's number can be derived through simple algorithms. The last 400 digits are these: 3881448314065252616878509555264605107117200099709291249544378887496062882911725063001303622934916080254594614945788714278323508292421020918258967535604308699380168924988926809951016905591995119502788717830837018340236474548882222161573228010132974509273445945043433009010969280253527518332898844615089404248265018193851562535796399618993967905496638003222348723967018485186439059104575627262464195387. 3881448314065252616878509555264605107117200099709291249544378887496062882911725063001303622934916080254594614945788714278323508292421020918258967535604308699380168924988926809951016905591995119502788717830837018340236474548882222161573228010132974509273445945043433009010969280253527518332898844615089404248265018193851562535796399618993967905496638003222348723967018485186439059104575627262464195387. Specific integers known to be far larger than Graham's number have since appeared in many serious mathematical proofs, for example, in connection with Harvey Friedman's various finite forms of Kruskal's theorem.#targetaudience #antitcc - @tuffguy5866