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A204845
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Irregular triangle read by rows in which row n lists primitive prime factors of the repunit (10^n - 1)/9 (A002275(n)).
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6
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1, 11, 3, 37, 101, 41, 271, 7, 13, 239, 4649, 73, 137, 333667, 9091, 21649, 513239, 9901, 53, 79, 265371653, 909091, 31, 2906161, 17, 5882353, 2071723, 5363222357, 19, 52579, 1111111111111111111, 3541, 27961, 43, 1933, 10838689, 23, 4093, 8779, 11111111111111111111111
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OFFSET
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1,2
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LINKS
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EXAMPLE
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Triangle begins:
1
11
3 37
101
41 271
7 13
239 4649
73 137
333667
9091
...
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MAPLE
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with(numtheory):
S:= proc(n) option remember;
`if`(n=1, {1}, S(n-1) union factorset ((10^n-1)/9))
end:
T:= n-> sort([(S(n) minus `if`(n=1, {}, S(n-1)))[]])[]:
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MATHEMATICA
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S[n_] := S[n] = If[n==1, {1}, S[n-1] ~Union~ FactorInteger[(10^n-1)/9][[ All, 1]]]; T[n_] := Sort[S[n] ~Complement~ If[n==1, {}, S[n-1]]]; Table[ T[n], {n, 1, 30}] // Flatten (* Jean-François Alcover, Mar 13 2017, after Alois P. Heinz *)
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CROSSREFS
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KEYWORD
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nonn,tabf
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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