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A081520
Triangle read by rows in which row n consists of 1 and the n-1 smallest positive numbers having common factors with n.
5
1, 1, 2, 1, 3, 6, 1, 2, 4, 6, 1, 5, 10, 15, 20, 1, 2, 3, 4, 6, 8, 1, 7, 14, 21, 28, 35, 42, 1, 2, 4, 6, 8, 10, 12, 14, 1, 3, 6, 9, 12, 15, 18, 21, 24, 1, 2, 4, 5, 6, 8, 10, 12, 14, 15, 1, 11, 22, 33, 44, 55, 66, 77, 88, 99, 110, 1, 2, 3, 4, 6, 8, 9, 10, 12, 14, 15, 16, 1, 13, 26, 39, 52, 65, 78
OFFSET
1,3
LINKS
EXAMPLE
1;
1, 2;
1, 3, 6;
1, 2, 4, 6;
1, 5,10,15,20;
1, 2, 3, 4, 6, 8;
1, 7,14,21,28,35,42;
...
MAPLE
arow:= proc(n) local L;
L:= select(t -> igcd(t, n) > 1, [$1..n^2]);
1, op(L[1..n-1]);
end proc:
seq(arow(n), n=1..20); # Robert Israel, May 21 2015
MATHEMATICA
Table[Join[{1}, Select[Range[n^2], GCD[n, #] > 1 &, n - 1]], {n, 1, 13}] // Flatten (* Ivan Neretin, May 21 2015 *)
PROG
(PARI) for(n=1, 5, print1("\n1"); for(i=1, n-1, print1(", "i*n))) \\ Charles R Greathouse IV, May 21 2015
CROSSREFS
KEYWORD
nonn,tabl,easy
AUTHOR
Amarnath Murthy, Mar 27 2003
EXTENSIONS
More terms from Ryan Propper, Nov 05 2005
Name edited by Robert Israel, May 21 2015
STATUS
approved