Zsbán Ambrus
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 Jul 16 comment What is the math behind the game Spot It? About the mathematical principles, see also David Madore's recent writeup "Le jeu de cartes Dobble et la géométrie projective expliquée aux enfants" madore.org/~david/weblog/… (note that "Dobble" is another for this game). See also math.stackexchange.com/q/464932/24908 , math.stackexchange.com/q/172771/24908 Jul 16 comment Are there an infinite set of sets that only have one element in common with each other? See also David Madore's recent writeup "Le jeu de cartes Dobble et la géométrie projective expliquée aux enfants" madore.org/~david/weblog/… Jul 16 comment Dobble card game - mathematical background See also David Madore's recent writeup "Le jeu de cartes Dobble et la géométrie projective expliquée aux enfants" madore.org/~david/weblog/… Apr 22 comment Analogue of Fáry's theorem taking sphere and geodesics instead of plane and straight lines. I guess it's true. Couldn't you draw any graph on the sphere by first drawing it on the plane, then copying the drawing to a very small part of the sphere where the great circle segments are very close to straight lines in the original drawing? Mar 20 awarded Commentator Mar 20 comment 4 Sided dice - flawed logic? I get 83/128 as the answer, slightly more than you. Mar 2 comment Identify subsets of $\mathbb{N}$ with their characteristic functions See also cross-post at mathoverflow.net/q/198807/5340 "Question about of comeager set" Dec 20 awarded Caucus Jun 25 awarded Informed Jun 16 awarded Critic Mar 8 comment What was the first bit of mathematics that made you realize that math is beautiful? (For children's book) I think it's more impressive that if you subtract one from that number, you get its reciprocial. Oct 22 answered Eleven unit squares inside a larger square May 15 comment Monochromatic triangles in a two-coloring of the plane This is posed as a difficult problem number 14.8 in Lovász László, Combinatorial Problems and Exercises, 2nd ed. You may check out the hints given there in the hints section. Mar 11 comment Number of integer solutions to $3i^2 + 2j^2 = 77 \cdot 6^{2012}$ I don't understand. So what if the ratio $i/j$ is neither 5 nor 5/3? Mar 9 comment What makes elementary functions elementary? That definition sounds wrong to me. By that definition, $\sin x = ax + b$ would have an elementary solution $x$ as a function of $a, b$. Mar 4 comment Need some help settling a bet Also, in the future, please try to use titles for your posts that help people browsing the titles to decide whether they might be able to help in your question. Eg. here you could use the title “Is there a power of two divisible by three?” or “Splitting pizza to three people evenly by repeatedly halving slices”. Mar 4 comment Puzzle: $(\Box @)+(\Box @) = (\Box\bigstar\Box$) @barf: it was probably downvoted because there's an earlier answer that seems complete enough. Mar 4 comment How many fours are needed to represent numbers up to $N$? By the way, if you allow logarithms, you don't even need four fours: actually three fours are enough to represent any positive integer like $\log\bigl(\log 4/\log(\surd\surd\dots\surd4)\bigr)/\log 4$. Feb 25 answered Convolution of the Möbius function with itself Feb 18 awarded Supporter