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erdős #1134

← #1133 · #1135 → (packet.json; erdosproblems.com)

Let $A \subseteq N$ be the smallest set which contains $1$ and is closed under the operations $x \mapsto 2 x + 1,$ $x \mapsto 3 x + 1,$ and $x \mapsto 6 x + 1.$ Does $A$ have positive lower density?

Worked, still open.

number theory · solved · prize £10 · 0 attempts

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A185661 — Smallest set containing 1 and closed under the operations x->2x+1, x->3x+1, x->6x+1.1,3,4,7,9,10,13,15,19,21,22,25,27,28,31,39,40,43,45,46,51,55,57,58,61,63,64,67,76,79,81,82,85,87,91,93,94,103,111,115,11

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solved

finding.noted · reviewer:will-blair · 1 day

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