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A126260 Irregular triangle read by rows where row n contains the positive integers k, k<=n, where every positive integer <=k and coprime to k is also coprime to n. 6
1, 1, 2, 1, 2, 3, 1, 2, 4, 1, 2, 3, 4, 5, 1, 2, 6, 1, 2, 3, 4, 5, 6, 7, 1, 2, 4, 6, 8, 1, 2, 3, 6, 9, 1, 2, 4, 10, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 1, 2, 6, 12, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 1, 2, 4, 6, 14, 1, 2, 3, 15, 1, 2, 4, 6, 8, 10, 12, 14, 16, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

The first term of each row is 1. The second term of each row, except for row 1, is 2. The last term of row n is n.

LINKS

Michael De Vlieger, Table of n, a(n) for n = 1..12325 (rows 1 <= n <= 300).

EXAMPLE

Table begins:

1

1,2

1,2,3

1,2,4

1,2,3,4,5

1,2,6

...

Row 10 is (1,2,4,10) because the positive integers <=1 and coprime to 1 are {1}, for 2 they are {1}, for 4 they are {1,3}, for 10 they are {1,3,7, 9}; and 1,1,1,3,1,3,7,9 are each coprime to 10.

MATHEMATICA

f[n_] := Select[Range[n], GCD[ #, n] == 1 &]; g[n_] := Select[Range[n], Times @@ GCD[f[ # ], n] == 1 &]; Flatten@Table[g[n], {n, 17}] (*Chandler*)

Table[Select[Range@ n, Function[k, AllTrue[Select[Range@ k, CoprimeQ[#, k] &], CoprimeQ[#, n] &]]], {n, 17}] // Flatten (* Michael De Vlieger, Aug 21 2017 *)

CROSSREFS

Sequence in context: A263939 A136311 A243884 * A264846 A265691 A214614

Adjacent sequences:  A126257 A126258 A126259 * A126261 A126262 A126263

KEYWORD

nonn,tabf

AUTHOR

Leroy Quet, Dec 22 2006

EXTENSIONS

Extended by Ray Chandler, Dec 24 2006

STATUS

approved

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Last modified July 23 04:24 EDT 2019. Contains 325232 sequences. (Running on oeis4.)